Denmark and Norway have condemned Syria for failing to stop attacks on their embassies in a row over the publication of contentious cartoons.
Syrians set fire to the Norwegian and Danish embassies in Damascus in protest at the publication of newspaper cartoons of the Prophet Muhammad.
The two Nordic countries said it was unacceptable that Syrian authorities had allowed protests to take place.
The two countries have called for their citizens to leave Syria.
The US also criticised Syria's approach, saying it was "inexcusable" for such damage to be inflicted on diplomatic missions.
"The United States condemns in the strongest terms the burning of the Danish and Norwegian embassies in Damascus, Syria today, which also damaged the Chilean and Swedish embassies," a White House spokesman said.
"The government of Syria's failure to provide protection to diplomatic premises, in the face of warnings that violence was planned, is inexcusable."
Protesters had scaled the Danish site amid chants of "God is great", before moving on to attack the Norwegian mission.
The cartoons sparked Muslim outrage across the world, following their publication in a Danish paper in September.
One depicts Muhammad as a terrorist. Any images of the Prophet are banned under Islamic tradition.
30 Sept: Danish paper publishes cartoons
20 Oct: Muslim ambassadors complain to Danish PM
10 Jan: Norwegian publication reprints cartoons
26 Jan: Saudi Arabia recalls its ambassador
30 Jan: Gunmen raid EU's Gaza office demanding apology
31 Jan: Danish paper apologises
1 Feb: Papers in France, Germany, Italy and Spain reprint cartoons
However, several European papers recently reprinted the cartoons, citing free speech.
The publications prompted diplomatic sanctions, boycotts and death threats in some Arab nations.
Two Jordanian editors who published the cartoons have been arrested.
Syrians have staged sit-ins outside the Danish embassy since the row intensified earlier this week, when Damascus recalled its ambassador.
Some removed the Danish flag and replaced it with another reading: "There is no god but God and Muhammad is the messenger of God."
The embassy was closed, and no diplomats were reported to have been injured in either attack.
Outside the Norwegian embassy, police fired tear gas to try to disperse the protesters, but some broke in and set it ablaze.
Demonstrators also tried to storm the French mission, but were stopped.
On Friday, the Danish prime minister made a new bid to calm anger, by explaining his position over the publication to Muslim ambassadors.
Anders Fogh Rasmussen said he could never apologise for a newspaper's actions, but said he was "distressed" at offence caused.