An Arab and Western-backed resolution condemning the violent crackdown in Syria has been vetoed at the UN Security Council by Russia and China. The two permanent council members rejected the draft resolution, which came hours after activists accused Syrian security forces of killing at least 55 people at Homs, BBC News informs.

The US ambassador said the vetoes were "shameful", Britain was "appalled".

China and Russia defended their move, saying the draft was "unbalanced".

Earlier, Russian Foreign Minister Sergei Lavrov criticised the draft resolution for singling out the government of President Bashar al-Assad, and not containing measures against armed opposition groups.

But proposed Russian amendments to the text were described as "unacceptable" by the US ambassador to the UN, Susan Rice.

Mr Lavrov is due to have talks with Mr Assad in Damascus on Tuesday, along with the head of the Russian Foreign Intelligence Service, Mikhail Fradkov.

In another development, Tunisia moved to sever relations with the Assad government.

We are travelling with a group of rebel fighters - the Free Syrian Army, as they call themselves. They first got news that a huge bombardment was taking place in the early hours.

They immediately started a "blood drive", attempting to take donated blood into the city to help out. But so far they've been unable to get that blood into Homs because the city has been cut off by checkpoints and tanks.

It's always difficult to get in to Homs, but after this, it is more difficult than ever. We're travelling on back roads to avoid the presence of checkpoints and tanks.

The information we're getting from inside the city is that mortar shells and tanks were used in what we're hearing was a pretty relentless bombardment in those areas that are outside of the regime's control.

The rebels now say that they're going to launch a general offensive some time in the next 24 hours in response to the attack.