Russia and China's UN Security Council veto has let the Syrian people down by backing President Bashar al-Assad's "brutal suppression", Foreign Secretary William Hague said Saturday.

Their action would only encourage further bloodshed, said Hague in a strongly worded statement responding to their veto of a UN Security Council resolution condemning the Syrian government's deadly crackdown on protests.

The UN vote came as activists accused Syrian troops of having killed more than 230 people in during the shelling of the city of Homs overnight.

"Russia and China faced a simple choice today: would they support the people of Syria and the Arab League or not?", Hague said.

"They decided not to, and instead sided with the Syrian regime and its brutal suppression of the Syrian people in support of their own national interests.

"Their approach lets the Syrian people down, and will only encourage President Assad's brutal regime to increase the killing, as it has done in Homs over the past 24 hours.

"The draft resolution, tabled by Morocco, supported Arab League efforts to resolve the crisis in Syria and called for an immediate end to all violence. It did not impose any sanctions, nor did it authorise military action.

"At every stage we worked to accommodate the concerns of some council members and tabled a text which did just that. There was nothing in the draft to warrant opposition.

"More than 2,000 people have died since Russia and China vetoed the last draft resolution in October 2011. Over 6,000 people have died in the 10 months since the uprising began. Many more have been tortured and detained.

"How many more need to die before Russia and China allow the UN Security Council to act?

"Those opposing UN Security Council action will have to account to the Syrian people for their actions which do nothing to help bring an end to the violence that is ravaging the country.

"The United Kingdom will continue to support the people of Syria and the Arab League to find an end to the violence and allow a Syrian-led political transition."

Thirteen countries voted for the UN Security Council resolution proposed by European and Arab nations to give strong backing to an Arab League plan to end the crackdown.