A group of 58 countries led by Switzerland on Monday expressed "strong support" for a French proposal to drag Syria before the International Criminal Court, a move expected to be nixed by Russia and China.

In a letter on behalf of the group, the Swiss ambassador to the UN, Paul Seger, urged the UN Security Council to adopt a draft resolution "to send a strong message of political support."

"The United Nations -- the Security Council and the wider membership alike -- should be united in acting for justice and accountability for the victims of the conflict in Syria," Seger wrote.

The United States did not sign the letter but supported the French proposal, diplomats said.

However, diplomats said China and Russia, a close Syrian ally, will likely veto the measure in a vote expected to take place Thursday.

If Beijing and Moscow exercise their veto power, it would be the fourth time they have done so on Western resolutions since the start of the Syrian crisis three years ago.

Western powers have decried mounting atrocities by the Syrian government on civilians said to include systematic torture, chemical attacks and the use of "barrel bombs" packed with explosives.

The conflict in Syria so far has killed 150,000 people and displaced nearly half the population.