Care is always in order when assessing defections. These are highly partisan acts that lend themselves to highly partisan interpretations. The precise details surrounding the departure of the Syrian Prime Minister, Riad Hijab, are unclear and may remain so. But the signals sent by his flight, which was described by his spokesman as a defection and by the official Syrian media as his dismissal – with some confusion about which came first – are unambiguous. President Bashar al-Assad's power is fracturing from within.

Mr Hijab was appointed only two months ago in what was seen as a belated effort by Mr Assad to broaden his government's appeal. No runes have to be read to conclude that this period of timid concessions is at an end. In the past month or so, the rate of departures has accelerated. Mr Assad has lost several senior diplomats, including the ambassador to Iraq and the chargé d'affaires in London; a senior military commander, General Manaf Tlas, from a family closely associated with the Assads; and dozens of military officers, including as many as 30 generals, who are said to have crossed the border into Turkey.

The violence, until recently restricted mainly to traditional areas of discontent, edges ever closer to the heart of Damascus. Three weeks ago, three senior members of the country's security establishment, including the Defence Minister and a brother-in-law of the President, were killed in an explosion that has still not been fully explained. Yesterday, a bomb was reported to have exploded in the Syrian state television and radio building. There is little evidence in any of this of a power structure that can carry credibility in the long term.

If time for Mr Assad and his ruling Alawite clan is running out, however, there must be profound trepidation about what comes next. Rebel forces have so far held out in Syria's biggest city, Aleppo, but government forces are inflicting nightly raids, tens of thousands of civilians have fled, and those remaining are bracing themselves for a concerted government assault. With Kofi Annan's resignation last week as special UN and Arab League envoy and the US promising assistance to the rebels, the last vestiges of the peace effort have fizzled out. The prospect of an all-out fight for Syria comes closer by the day.

This alone should concentrate minds on the dire repercussions of such a conflict, and of neighbours – such as Iran – being drawn to fish in increasingly murky waters. Mr Annan may have resigned his commission, finding insufficient will on either side to observe the ceasefire he so painstakingly negotiated, but this does not absolve the wider international community, in the shape of the UN Security Council and Syria's neighbours, of a duty to try one last time to avert the bloodbath that increasingly looks inevitable.

As recent footage of killings by the Free Syrian Army indicates, the conflict is becoming something far more complicated than a heroic uprising against a malevolent and doomed regime – as will be the consequences. This does not in any way diminish President Assad's responsibility, least of all for using violence against his own people in a desperate effort to stay in power. It does mean, though, that any framework for a post-Assad scenario must make demands of all sides.

So far, the only consensus reached was in the UN General Assembly at the end of last week, which censured the Security Council for its failure to stop the violence in Syria. The chances that this will galvanise the Security Council to try again may be slim. But if hope of mediating an orderly transition is fading, perhaps fear – fear of what failure could mean, for Syria and for the region – will finally persuade the Big Five, including China and Russia, to act as one.