The bomb at the National Security headquarters in Damascus yesterday struck a potentially fatal blow at the heart of the Assad regime.

Within hours of the blast that killed the Defence Minister, a general and the President's brother-in-law, Syria's Information Minister was on television to denounce the "terrorists". But the more he blustered about the malign hand of foreign intelligence services and the continued strength of the Syrian army, the Syrian people and the Syrian state, the clearer the sense of a regime with control slipping from its blood-stained fingers.

Little matter who among the country's fragmented opposition was responsible for the blast (in the immediate aftermath, it was claimed by several). That a bomb could be planted inside the National Security building, and kill a relative of the President, is the strongest possible signal that the ruling regime is no longer impregnable, that it can no longer guarantee the safety of its own.

For the rebels, the boost to morale will mean much, not least after the appalling violence in Tremseh last week and government forces' continued defiance of Kofi Annan's peace plan. The message is more potent still for the President's backers. Despite all the bloodshed, the Assad family still enjoys a level of public support. When that melts away, it is the beginning of the end. And it will happen fast if the regime starts to look like it is losing.

All this on the eve of yet another attempt at a UN resolution, in the hope of resuscitating the Annan plan. Despite reassurances that the focus is sanctions, not military intervention, Russia and China are as wary as ever and there is little hope of consensus. It may no longer matter. For all the Foreign Secretary's claims that yesterday's events confirm the urgent need for UN action, in fact the situation in Syria has taken on a dynamic of its own, one that is rapidly outstripping the international community's capacity to respond.

With the army bent on vengeance, and the regime fighting for its life, the immediate outlook in Syria is grim indeed. But it is for President Assad that it is grimmest of all.