Syrian President Bashar Al Assad can be classified as a war criminal, US Secretary of State Hillary Clinton said as the United Nations announced more than 7,500 civilians had been killed by his forces since the start of the revolt.
At least 25 people were killed in the shelling of opposition strongholds by Syrian forces on Tuesday, activists said. In Homs alone, opposition groups said hundreds of civilians had been killed or wounded in the 24-day-old assault.
"There would be an argument to be made that he would fit into that category," Clinton told a Senate committee hearing on Tuesday. She added however that using such labels "limits options to persuade leaders to step down from power".
As world dismay grew over the bloodshed, France said the Security Council was working on a Syria resolution and urged Russia and China not to veto it, as they have previous drafts.
In the besieged district of Baba Amro and other parts of Homs, terrified residents were enduring dire conditions, without proper supplies of water, food and medicine, activists said.
A wounded British photographer managed to escape from Homs but the fate of French reporter Edith Bouvier was not clear.
"There are credible reports that the death toll now often exceeds 100 civilians a day, including many women and children," UN Under-Secretary-General for political affairs
Lynn Pascoe told the UN Security Council. "The total killed so far is certainly well over 7,500 people."
Syria's government said in December that "armed terrorist groups" had killed more than 2,000 soldiers and police.
French Foreign Minister Alain Juppe had said on Monday it was time to refer Syria to the International Criminal Court and warned Assad that he would face justice.
He told the French parliament work had begun at the Security Council on a new resolution. "I solemnly call on Russia and China not to block this Security Council resolution," he said.
Russia and China vetoed a draft resolution on Feb 4 that would have backed an Arab League call for Assad to step down.
UK Foreign Secretary William Hague said he had discussed the situation with former UN Secretary-General Kofi Annan, now the UN-Arab League envoy on Syria, saying he hoped Annan would "bring his persuasive powers to bear on Russia and China".
Syria's UN ambassador in Geneva, Faysal Khabbaz Hamoui, stormed out of the UN Human Rights Council after calling on countries to stop "inciting sectarianism and providing arms" to Syrian rebels.
He said foreign sanctions were preventing Damascus from buying medicines and fuel. The European Union imposed additional punitive measures on Tuesday.
British photographer Paul Conroy, of London's Sunday Times, was spirited safely out of Homs into Lebanon. "He is in good shape and in good spirits," the newspaper said.
Conroy had been among several foreign journalists trapped in Baba Amro, where Marie Colvin, a veteran war correspondent also with the Sunday Times, and French photographer Remi Ochlik were killed in a bombardment on Feb. 22.
Confusion surrounded Bouvier's fate. President Nicolas Sarkozy initially said he had been informed that Bouvier had been evacuated, but later said that had not been confirmed.
The latest bombardment of Baba Amro was the heaviest so far, activists said, adding tanks from an elite armoured division led by Assad's brother Maher had moved into Homs overnight.
The Syrian Observatory for Human Rights said at least 16 people were killed in Homs on Tuesday, a day after 84 were killed in the city, out of an overall death toll of 122 civilians across Syria. The British-based group said 29 security force members had been killed in clashes with rebels on Monday.
In Hama province, security forces bombarded the town of Helfaya, a centre of anti-Assad protests, killing 20 people.
The reports could not be independently confirmed. Syrian authorities tightly restrict media access to the country.
The International Committee of the Red Cross said it had delivered food and other aid to Homs and Idlib, but called for a "humanitarian ceasefire" to improve access.
Assad, projecting an aura of normality in a land ravaged by conflict over his right to power, promulgated a new constitution on Tuesday after officials said nearly 90 percent of voters had endorsed it in a referendum two days earlier. Opposition groups and Western leaders seeking his removal denounced it as a sham.