Libya: The challenges facing allies
Defence sources say forces loyal to Libyan leader Col Gaddafi are starting to feel the pinch on their arms supply as the coalition air campaign "chops the legs" off their already-stretched supply chain.
A long-range bombing raid by US and British warplanes earlier this week destroyed a major ammunition dump storing small arms and artillery munitions.
Home to some 40 concealed underground bunkers, the coalition believes it could have been used by pro-Gaddafi forces against civilians in areas such as Misrata and Zintan in the north.
"With highly targeted strikes like this we are hitting Gaddafi's forces where it hurts, limiting their supply lines and in turn reducing their capability to kill their own civilians," said UK Defence Secretary Liam Fox.
"Over the last few days UK jets over the skies of Libya have taken out a lot of Gaddafi's military assets, including air defence systems, tanks and armoured personnel carriers, in line with the [UN resolution]."
Military sources say that the coalition's air strikes so far have ensured the regime's forces have been "seriously degraded". However, there are indications that further air strikes on military ammunition dumps or forces attacking towns are likely to continue, as "there is more to do to prevent more loss of life".
As the fighting in and around key towns in Libya continues, it is also believed that Col Gaddafi's loyalists are still recruiting more foreign fighters or mercenaries from outside Libya, from countries such as Chad, Mali and Niger, and using them mainly to control urban areas.
All this seems to indicate that while the coalition's strikes may have successfully removed many of the larger weapons in the pro-Gaddafi forces' armoury, much of their command and control and the majority of air defences, the hope that Col Gaddafi's regime would crumble rapidly from within has not been fulfilled.
Much depends on the rebels themselves, but they have so far shown little sign of becoming more organised. They, too, are starting to run low on ammunition, prompting fierce debate in Washington, London and elsewhere over the possibility of arming them.
Their supply chain - where and if it exists - is much shorter, and they are only lightly armed, but most lack any training, so that giving them weapons of any sophistication would run into immediate difficulties.
It's acknowledged that in military terms, they are no match for Col Gaddafi's forces at a very basic level. And as they are pushed back from some of their earlier gains over the weekend, morale amongst many will be getting shakier.
Although some within the opposition are defectors from the regular forces, most are armed civilians with little experience of the battlefield - and they appear to have little discipline or leadership, or the ability to co-ordinate their movements and aims.
Pressure on Gaddafi
The coalition is now also trying to find out more about who exactly the rebels are, as fears about their composition emerged publicly in Washington on Tuesday when Nato's military commander in Europe, Admiral James Stavridis, told a Senate hearing that there were "flickers" in intelligence reports about the presence of al-Qaeda and Hezbollah members among the anti-Gaddafi forces.
He said Nato was "examining very closely the content, composition, the personalities... the leaders of these opposition forces."
The aim of the military campaign is to keep up sustained pressure on the Libyan regime, as command of the coalition is transferred to Nato.
However, the coalition can only do so much from the air and from the sea without putting in ground forces - and defence sources in the UK say they have been clear from the start that there is "no request for, and no intention for ground forces".
So, a lot will depend on the kind of political and diplomatic pressure that can be exerted on Col Gaddafi and his supporters.
The coalition's best hope must remain that his forces and regime will lose heart before the opposition does, as the military mission moves in conjunction with political overtures seeking to encourage the Libyan leader to flee the country - so far, unsuccessfully.
However, the coalition's own room for manoeuvre on the military front is itself time-sensitive. Already, countries such as Russia have expressed fears that the operation is over-stepping the UN mandate, while China, Russia and Germany are all against arming the rebels.
The fragile consensus that binds the coalition - and its Arab supporters - together could easily be shattered by any such move.
But unless the coalition does supply arms, or facilitate that, it is becoming harder to see how the rebels can win, or how Libya can avoid the prospect of a lengthy stand-off between the Col Gaddafi loyalists and a disorganised opposition.
Another danger is of reprisals by Libyan forces loyal to Col Gaddafi, and the risk of continuing low-level urban warfare inside populated areas in Libya, which could itself endanger civilian lives as the balance teeters back and forth between the two sides.
A prolonged stalemate is the outcome that the coalition was keen to avoid, along with the prospect of limited military action turning into a longer campaign to enforce the no-fly zone while a weakened but still influential dictator in Tripoli shows the limits of military intervention - not least as western leaders seek to banish the spectre of Iraq.