Analysis: Syria's complex and bloody crisis
There are few certainties or even probabilities in the complex and bloody crisis in which Syria is now mired.
It is uncharted terrain for all - the regime itself, its population, its fellow Arab states, non-Arab neighbours Turkey and Israel, and the concerned outside world. Huge issues are at stake in the deepening struggle.
The collapse of the regime and a descent into chaos, in a country where sectarian and ethnic fault lines converge, would have huge repercussions in the wider region.
It would redraw its geopolitical map. Iran would stand to lose a vital channel for support to its ally in Lebanon, Hezbollah. Russia would likely lose its most important Arab ally.
And the possible emergence of a Sunni-led Syria, perhaps dominated by Islamists as seems to be happening in Egypt and elsewhere, would not necessarily be good news for the West and Israel either.
'Crushing the rebels'
One thing that seems relatively safe to predict is that the regime's current drive to crush armed rebels will continue until it has secured control of areas which had slipped out of its grasp in recent months.
It formally committed itself to that goal - at least for Homs and its province - in an interior ministry statement on Monday night.
The subsequent visit to Damascus by the Russian Foreign Minister, Sergei Lavrov, has clearly done nothing to curb the onslaught.
In fact, the campaign goes far beyond Homs and its environs.
It was launched a few days after the Arab League's foreign ministers met in Cairo on 22 January and adopted a new peace plan for Syria, which called on President Bashar al-Assad to hand power to his vice-president and make way for the rapid formation of a national unity government including the opposition.
Change of Arab plan
That implicitly scrapped an earlier Arab peace plan, adopted on 2 November, which Syria accepted and which it and Russia still support.
The November scheme called for an end to violence from whatever source, the withdrawal of armed forces, the deployment of Arab observers, the release of detainees, and rapid movement towards national dialogue.
The sudden adoption of a radically different plan, and the move to take the issue to the UN Security Council, apparently convinced Mr Assad that Syria's powerful Arab adversaries - notably the Saudi-led Gulf states and especially Qatar - backed by Western powers, would stop at nothing to overturn his regime.
Damascus had already accused those Arab powers of arming and financing rebel groups, with guns and money pouring into the country across porous borders from Turkey, Lebanon, Jordan and Iraq.
So the crackdown launched by Syrian security forces after the unveiling of the new Arab League plan is aimed at bringing key population centres back under government control, eliminating the armed opposition, and securing borders to stop the flow of weapons and money.
It has seen troops drive armed rebels out of the suburbs of Damascus itself, and put severe pressure on them in other places where they have taken root - Homs, Hama, Idlib, Deraa and elsewhere.
BBC correspondent Paul Wood's reports from inside Homs
Homs and Hama are strategically important because they control the highway between Damascus and Aleppo, the two big cities which have yet to be fully caught up in the revolt. Homs is also close to the Lebanese border.
Idlib and its province in the north-west are important because they are adjacent to Turkey, where the rebel Free Syrian Army is based.
In recent days security forces have been on the move in towns, villages and country areas near all four borders, attacking any centres of armed resistance they can find.
Lebanese analysts well versed in Syrian affairs believe that, far from disapproving of the crackdown on armed rebels, the Russians may even have encouraged it.
But neither the Russians nor the regime itself can seriously think that crushing or curbing armed groups represents a solution to the entire crisis.
Compromise and agreement
Moscow is said to believe that "armed extremist groups" need to be eliminated because they would sabotage any compromise agreement reached through dialogue between the regime and its opponents.
By that reading, the current escalation would be more about affecting the balance of a future post-crisis Syria than pursuing the illusion that the entire uprising could be defeated by force, and that things would go back to how they were, as though nothing had happened.
As the continued defiance at Homs, Hama, Deraa and elsewhere have shown, it is not that easy.
Although the escalation looks set to continue, it is not a comfortable time for Russia.
After the Russian and Chinese veto of an otherwise unanimous Security Council resolution that would have adopted the second Arab League peace plan, with its call for Mr Assad to step aside, the powers that supported the torpedoed resolution are urgently seeking another way forward.
'Militarising' the conflict
Although there are no obvious answers, that process is bound to intensify and speed up the longer the bloodbath continues and the uglier it gets.
Although external military intervention, as was seen in Libya, is being constantly ruled out, there is mounting pressure for some kind of action to halt the carnage, and ideas such as the creation of protected corridors for humanitarian aid, or safe-havens of some sort, are being increasingly discussed.
The creation of some kind of formal or informal coalition of powers to support the Syrian opposition has been proposed in different forms by a variety of quarters, including the US, UK, and Turkey.
That is far from being a straightforward proposition. Both politically and militarily, the opposition is divided.
The main umbrella group in exile, the Syrian National Council (SNC), has failed to unify with other opposition factions and agree on a shared platform.
While it has generally supported the Free Syrian Army, it came under a blistering attack from the FSA commander, Col Riyad al-Asaad, just as the violence at Homs was reaching a crescendo.
The FSA itself faced a challenge from a new military body, the Supreme Military Council, set up this week under a more senior defecting officer, Gen Mohammed al-Sheikh, who has also installed himself in southern Turkey.
But these are wrinkles that could be smoothed out quickly under the pressure of time, events and a strong will from outside powers.
And even if not, if the drive for an international consensus over Syria is abandoned, there is a strong danger from Russia's viewpoint that the existing level of clandestine outside support to opposition rebels will be greatly stepped up, plunging the country into chaos and fragmentation, and clinching Moscow's loss of its most important Arab ally.
The Russian calculation may be that it is better to use its undoubted influence with Damascus - with which it has a strategic relationship going back decades into Cold War and Soviet times - to play a leading role in brokering a Syrian settlement within an international consensus.
That is presumably why President Dmitry Medvedev, in conversations with Turkish Prime Minister Recep Tayyip Erdogan this week, continued to propose the Security Council as the proper forum for elaborating an agreed strategy, despite the Russian-Chinese veto.
Even the Syrian National Council, despite fury at the veto, has not ruled out a Russian role.
"Russia remains a potential mediator," the SNC said in its latest statement. "[But it must] first use its influence on the regime in order to stop the killings immediately."
"A negotiated transition can only come afterwards, and will need to encompass the stepping aside of the head of the regime, a demand for which thousands of Syrians have died."
These two key demands are likely to be the focus of intense scrutiny as all sides consider their options under the pressure of events on the ground.
They imply that the regime has been defeated and must step aside - something that it is not ready to concede, apparently supported by Moscow.
Remaining support for Assad
The situation is far more complex than during the uprisings in Tunisia, Egypt and Libya.
In contrast to their ousted leaders, it does appear that the Assad regime still enjoys the support of significant sectors of the country's patchwork society, increasingly polarised as the crisis deepens.
By and large, his own Alawite minority apparently continues to stand with him, some no doubt fearful of the consequences of change.
The same seems generally to be true of other minorities, especially the Christians, with more questionable allegiance from the Kurds and Druze.
Secular-minded and business circles within the middle classes of the majority Sunni community, especially in the two biggest cities, have also shown little enthusiasm for the revolt, which some fear might bring Islamists to the fore, especially now that armed action is increasingly in the picture.
The regime has also apparently been able to continue using the army and security forces in a repressive role without them going to pieces. There have been individual or group defections on the ground, but not by whole units.
What nobody knows - probably not even the regime itself - is how long it can go on using forces in which the rank and file are necessarily largely Sunni, to quell a largely Sunni-based revolt.
That may be one of the key constraints forcing the regime towards an eventual compromise.
If there is to be a chance of a peaceful transition, a Russian role might be vital in persuading the regime to give ground - something Moscow would likely only do if it were convinced that a balanced outcome, rather than a Western-dictated formula removing Syria from its sphere of influence, would result.
Other formulae being explored, such as the idea of an enhanced, joint UN-Arab League observer mission and the appointment of a special envoy, would imply an international consensus and agreement to stabilise the situation.
A UN observer mission could not be mounted without a resolution from the Security Council, which Russia and China would have to approve.
It could also not be deployed without Syrian approval, because observers are not mandated or equipped to fight their way in or impose anything, just to monitor, report, and hope that their presence has a calming and restraining effect.
As the powers consider all these complexities, the killing on the ground goes on, with every drop of blood shed - on either side - making a solution and eventual reconciliation more difficult.