Syrian ceasefire leads to new challenges
Tough though it has been, getting agreement on the ceasefire in Syria is the easy bit compared with what comes next.
The truce itself has been shaky, and has more or less completely collapsed in some areas, especially those, mainly Sunni, quarters of Homs such as Khaldieh where rebel fighters are still entrenched and where hostilities and bombardment have reached close to pre-truce levels.
Just shoring up the ceasefire and preventing a major eruption of fighting across the board will in itself be a huge challenge.
Even before the advance party of UN monitors began arriving on Sunday night, there were ominous signs.
The government - through an "authorised military source" - said that "terrorist armed groups" had escalated the violence in a "hysterical" manner as soon as the Security Council passed its resolution on Saturday authorising the deployment of the first 30 truce observers.
It said the security forces would take action to prevent further "criminal attacks" by the "terrorist groups" - in other words, the ceasefire could effectively be discarded wherever the authorities deemed fit.
Opposition groups, including the Local Co-ordination Committees and the Muslim Brotherhood, called for a strict timetable for implementation of all six clauses of Kofi Annan's peace plan, and warned that the opposition could not remain committed indefinitely to "an empty truce" if the regime continued violations and the wider process was not implemented.
So, with many violations reported by both sides in many places apart from Homs, it is clear that the truce could collapse completely unless reinforced by implementation of the six-point Annan plan and the deployment of observers, whose presence, the UN hopes, may help deter or inhibit acts of violence.
At this point, the key question could be: in whose interest is a ceasefire that holds on the basis of implementing all points of the Annan plan?
The objective answer is that it is not to the regime's advantage - indeed, it could prove fatal.
But it would benefit the opposition, or at least those elements of it who want a peaceful settlement short of the violent overthrow of the regime, which is far from being a realistic possibility at present.
One of the key provisions of the plan is the return to barracks of the armed forces, with their tanks and heavy weaponry - a withdrawal that was supposed to be completed by last Tuesday as the first step in the ceasefire process, before even the truce itself came into effect.
It hasn't happened, and for good reason. The regime is only maintaining its grip in many areas by military force.
If that iron fist is relaxed, it risks losing control of a large proportion of the country, whether to armed rebel groups whose movements are hard to prevent, or simply to a defiant and dissenting populace in the many places where hearts and minds have long been lost.
That could create a momentum which might carry through to the two big urban centres that have not yet been fully caught up in the revolt but where trouble has been on the rise, Damascus and Aleppo, with potentially fatal consequences for the regime.
That is why the government, having initially accepted the Annan plan, suddenly baulked and came up with a new raft of conditions and demands, including that the rebels must agree to disarm, that the opposition must give written guarantees of compliance, and that outside states such as Saudi Arabia, Qatar and Turkey must also give formal pledges to stop backing the rebels.
In other words, a complete capitulation by the opposition, which would then enter any settlement talks in an extremely weak position, with the regime more or less free to dictate terms.
By contrast, a ceasefire in situ - as is theoretically in force right now - leaves rebel fighters in control in some parts of Homs and of Idlib province.
Despite the ferocity of the crackdown unleashed in late January, the regime has not been able fully to restore its control over all areas by force.
If the Annan plan is implemented in full, regime dominance of the balance of power would be redressed even more towards some kind of equilibrium with the opposition, so that talks would take place on some kind of level playing-field.
There is much evidence that Russia is playing an absolutely crucial role in bringing about what regime compliance there has been so far.
Moscow was instrumental in persuading Syria to accept the Annan plan in the first place, and then to drop the 11th-hour conditions it suddenly came up with.
That shows clearly that, while it can resist Western pressures and sanctions indefinitely, Damascus has no option but to bend when the Russians - with China tagging along - insist something must be done.
What is equally clear is that more pressure from Moscow will be needed if all clauses of the Annan plan are to be implemented, especially the withdrawal of troops, tanks and heavy weapons.
The Russian role will clearly be equally crucial when, and if, it comes to dialogue between the regime and its opponents. In many ways, Moscow will be the arbiter.
The alternative is stark: a return to the battlefield, with the regime trying to complete its control by force, and the opposition and its outside backers stepping up the arming and financing of rebel fighters, plunging the country into deep and prolonged chaos and a potential fragmentation that would have regional consequences.
That would not be in the interest of Russia or the regime's other outside allies, such as the Chinese and indeed Iran. They would risk losing their key Arab ally to an abrupt regime change pushed by regional and international rivals such as Saudi Arabia and the West.
So Russia is strongly motivated, and uniquely placed, to help act as midwife to political transition in Syria.
What exactly Moscow has in mind as an endgame is not clear but will obviously be important.
It could be something akin to the transition from the Soviet Union to the Russia of today.
Or perhaps Moscow sees it as a question of holding the ring while the Syrians themselves hammer out some kind of formula that would accommodate both the opposition and those still substantial sections of Syrian society that may still see the regime as a better alternative than sectarian chaos.
What is clear is that Russia does not buy into the idea that President Bashar al-Assad and his inner circle can simply crush dissent by force and implement "democratic reforms" that remain cosmetic and leave the core of the regime intact.
Work also needs to be done on the other side of the equation.
If a settlement is to have a chance, the opposition and its outside backers must be induced to give up their demand that Mr Assad must stand down as the first step in a transition process, and they must agree to talk to the regime.
In that sense, the Annan plan provided a face-saving way out for the Americans and others who had adopted the regime-change demand without having the means to bring it about swiftly or cleanly.
It also means that regional powers like Saudi Arabia and Qatar, who are engaged in a regime-to-regime vendetta with Damascus, would have to shelve their own ambitions, at least for the moment.
A successful peaceful resolution in Syria will depend strongly on a continuation and strengthening of the international consensus and collaboration that allowed the Security Council finally to pass its first resolution on the Syria crisis on Saturday, covering the initial deployment of 30 observers.
But negotiations on the country's future remain a distant prospect as the smoke of war continues to hang over Homs and other places. The situation on the ground clearly must first be stabilised, at least relatively.
A daily struggle can be expected over consolidating the ceasefire and implementing the Annan plan's provisions.
Nothing will come easy. The process involves a regime that is fighting for its survival and has shown it will stop at nothing to stay in power. So the chances are that pressure will have to be applied every step of the way.