Human rights campaigners have said that security forces have shot dead at least 70 protesters during anti-government rallies in Syria.
Many of the deaths occurred in the capital, Damascus, and in a village near Deraa in the south.
It is the highest death toll in five weeks of unrest against the Syrian President Bashar al-Assad.
In a statement, a White House spokesman called on the Syrian government to stop the use of violence against protesters and to follow through on promised reforms.
In a concession to the demonstrators earlier this week, President Bashar al-Assad ended five decades of emergency rule.
Before today's violence rights groups had said more than 220 people had been killed since unrest broke out on 18 March in Deraa.
As in the Tunisian and Egyptian revolutions that ousted Hosni Mubarak and Zine al-Abidine Ben Ali, citizens are rebelling against both a lack of freedom and opportunity and security forces' impunity and corruption that has enriched the elite while one-third of Syrians live below the poverty line.
