Protesters loyal to Syrian President Bashar Assad briefly broke into the US embassy in Damascus on Monday, while security guards at the French embassy used live ammunition to prevent them gaining access, diplomats told Reuters.
No casualties were reported in the attacks, which followed a visit by the US and French ambassadors to the city of Hama last week in support of the hundreds of thousands of pro-democracy demonstrators there despite a harsh crackdown by Assad gunmen.
Assad accused the United States - and Ambassador Robert Ford - of trying to incite the populace against his regime, also saying the US flag was flown in support of the protesters.
But State Department officials on Monday formally condemned Syria for failing to protect the US embassy complex in Damascus from a violent assault it said was encouraged by a pro-government Syrian television station.
"A television station that is heavily influenced by Syrian authorities encouraged this violent demonstration," the State Department said in a statement.
"We strongly condemn the Syrian government's refusal to protect our embassy, and demand compensation for damages. We call on the Syrian government to fulfill its obligations to its own citizens as well," the statement said.
"We are calling in the Syrian charge [d'affaires] to complain," said the US official, who spoke on condition of anonymity. "We feel they failed [in their responsibility to protect US diplomats]."
Some observers, however, question why US embassy security did not - as French security officers did - use live ammunition to protect the embassy themselves.
Human rights groups say at least 1,400 civilians have been killed since an uprising began in March against Assad's autocratic rule, posing the biggest threat to his leadership since he succeeded his father 11 years ago.
In other violence on Monday, Syrian forces killed one civilian and wounded 20 in heavy-machine gun fire on Homs, Syria's third city, and went house-to-house arresting suspected opponents in Hama, human rights activists said.
Despite using force to crush the protests, Assad has also called for talks on reforms. But many opposition figures have refused to attend a two-day conference in the capital, saying it was futile as long as violence continued.
"Dialogue can only work when both parties respect each other and look at each other as equals," said Ayman Abdel-nour, the Gulf-based editor of all4syria.com website. "At the moment, there is no dialogue."