Russia has signed a peace deal to end the conflict in Georgia but said "extra security measures" were needed before a withdrawal could begin.

Russian President Dmitry Medvedev added his signature to a French-led peace plan already endorsed by Georgia and by leaders of the two rebel regions at the heart of the conflict.

US President George Bush, speaking in Texas, said it was a "hopeful step" but that Moscow must now pull its forces out.

Russian Foreign Minister Sergei Lavrov said withdrawal would depend on the extra security measures ordered by President Medvedev, the nature of which was not made clear.

Asked how long the withdrawal might take, Mr Lavrov said: "This does not just depend on us" and blamed the difficult situation on the ground for delays.

The French-led agreement drafted this week authorises Russian forces to take extra security measures on a temporary basis pending the arrival of international peacekeepers - which requires a UN Security Council resolution.

Russian troops withdrew from an area 30 miles from the Georgian capital on and a foreign military observer said it appeared a partial pullout might be under way, although that was not officially confirmed.

Meanwhile accusations of violence on the ground has continued.

Georgia accused Russian troops of severing the country's main east-west train link by blowing up a railway bridge in broad daylight.

Russia's General Staff denied attacking the bridge, saying it regarded hostilities as over.

Russia's Colonel-General Anatoly Nogovitsyn, deputy chief of the General Staff, said: "We are now in peacetime. Why should we be blowing up bridges when our job is to restore? This therefore can only be yet another completely unverified statement."

British Foreign Minister David Miliband has welcomed Mr Medvedev's signing of the peace plan and said it must be "speedily and fully implemented", but denounced Russian "aggression" against Georgia and threats to neighbouring states.

A simmering conflict between Georgia and Russia erupted into war nine days ago, when Tbilisi launched an assault to retake its separatist province of South Ossetia, prompting a huge counter-offensive from Moscow, which supports the rebels.

Russia says 1,600 civilians died when Georgia stormed South Ossetia, though the figure has not been independently verified.

Georgia says at least 175 people have been killed and hundreds more injured. The figure does not include South Ossetia.

© Independent Television News Limited 2009. All rights reserved.