At least 2,000 people have been killed by government forces in Syria, Hillary Clinton has said, amid growing international condemnation of the crackdown against opposition protesters.
"We think, to date, the government is responsible for the deaths of more than 2,000 people of all ages," the US Secretary of State said.
She added that Syrian President Bashar al-Assad had "lost his legitimacy to govern the Syrian people".
Her comments came during a news conference with John Baird, the visiting Canadian Foreign Minister, and hours after the White House press secretary said the Syrian president was on his "way out".
On Thursday human rights group Avaaz said 109 Syrians had been killed in the besieged city of Hama, where tanks and troops have reportedly occupied a central square.
Hundreds are said to have died in the city since Sunday, when news of a brutal crackdown emerged.
However it has been difficult to ascertain a reliable death toll from the city as independent news agencies have been denied access.
Avaaz said many of the dead bodies had short-range bullet wounds, usually to the head. A Hama resident told CNN that many injured people are dying in hospital because they are without supplies and electricity.
Communications, electricity and water remain cut off, while residents are growing short of food and medical supplies. groups and witnesses said.
The UN Security Council condemned the violence earlier this week, saying those responsible "should be held accountable", while the European Union strengthened its sanctions against Syria.
Britain's Foreign Secretary William Hague also called on Assad's government to "end its violence and to allow genuine political reform".
A ruling decree on Thursday from Assad allowing a multi-party system has been met with suspicion from human rights groups and activists within the country.