BEIRUT - Hundreds of Syrian government supporters attacked the US Embassy in Damascus Monday, smashing windows and spray-painting walls with obscenities and graffiti that called the American ambassador a "dog." Guards at the French Embassy fired in the air to ward off another group of protesters.

The sharp escalation in tensions followed a visit last week by the American and French ambassadors to the city of Hama, a stronghold of opposition to authoritarian President Bashar Assad. Syrian authorities were angered by the visit and American Ambassador Robert Ford's harsh criticism afterward of the government crackdown on a four-month-old uprising. Ford's residence was also attacked on Monday.

The US and France both accused Syrian forces of being too slow to respond and demanded the government abide by its international obligations to protect diplomatic missions and allow envoys freedom of movement. The US formally protested, calling the attacks "outrageous," and saying protesters were incited by a television station heavily influenced by Syrian authorities.

"Ford get out now," protesters wrote on a paper hung on the US Embassy's fence. "The people want to kick out the dog," read graffiti scrawled in red on the wall of the embassy, along with another line cursing America. The protesters smashed the embassy sign hanging over one gate.

The US said it would seek compensation for damage.

Syrian-US relations have been mired in mutual distrust for years. But Monday's attacks were the worst such violence since 2000, when a stone-throwing mob attacked and vandalized the US Embassy and ambassador's residence over American and British airstrikes against Iraq.

The attacks pose a renewed challenge to the Obama administration. The White House has criticized the Syrian regime's violent crackdown on peaceful protests but has refrained from calling for an end to the Assad family's four decades of rule, seemingly wary of pressing too hard as it tries to wind down wars in Iraq and Afghanistan and faces criticism for being part of the coalition battling Moammar Gadhafi in Libya.

The US said about 300 "thugs" breached the wall of the embassy compound before being dispersed by American Marine guards. No injuries were reported.

State Department spokeswoman Victoria Nuland said the mob got onto the roof of the chancery building, spray-painted graffiti and broke windows and security cameras. They lobbed fruits and vegetables at the compound.

A witness told The Associated Press that protesters scaled a fence, smashed windows and raised a Syrian flag at the embassy.

Nuland said that Syrian security forces, who are supposed to guard the mission, were slow to respond.

After the crowd at the embassy was dispersed, the protesters moved to the ambassador's residence and attacked it, causing unspecified damage, Nuland said. The ambassador's residence is not inside the embassy compound but is nearby.

"We consider that the Syrian government has not lived up to its obligations ... to protect diplomatic facilities and it is absolutely outrageous," she told reporters.

There were similar scenes at the French embassy, where guards fired in the air to hold back Assad loyalists who attacked the compound.

The French Foreign Ministry said three embassy workers were injured as "well organized groups" smashed windows and destroyed the ambassador's car.

"Faced with the passivity of security forces, embassy security agents were forced to make three warning shots to stop intrusions from multiplying," a French government statement said.

The French flag was removed and replaced with a Syrian one.

"God, Syria and Bashar. The nation that gave birth to Bashar Assad will not kneel," read graffiti scrawled outside the embassy.

One witness said three protesters were injured when guards beat them with clubs. The witness asked not to be identified because of the sensitivity of the situation.

Hiam al-Hassan, a witness, said about 300 people were at the French Embassy while hundreds targeted the American diplomatic compound.

"Syrians demonstrated peacefully in front of the French embassy but they were faced with bullets," said al-Hassan.

Another protester at the French Embassy, Thuraya Arafat, 58, said: "I am here to find out why the French ambassador visited Hama. Did he go there to meet armed gangs?"

French Ambassador Eric Chevalier and Ford both made separate visits to Hama on Thursday.

Ford was greeted by friendly crowds who put flowers on his windshield and olive branches on his car, chanting: "Down with the regime!" The State Department said the trip was to support the right of Syrians to demonstrate peacefully.

Syrian authorities called the ambassadors' visits to Hama interference in the country's internal affairs and accused the envoys of undermining Syria's stability.

On Sunday, Ford attacked the government for allowing its supporters to demonstrate while violently suppressing anti-regime demonstrators.

"And how ironic that the Syrian Government lets an anti-US demonstration proceed freely while their security thugs beat down olive branch-carrying peaceful protesters elsewhere," he said.

On Sunday, the State Department complained that pro-government demonstrators threw tomatoes, eggs and rocks at the embassy over the weekend to protest Ford's visit to Hama.

Secretary of State Hillary Rodham Clinton said Monday that the attacks demonstrated the Syrian president was not serious about reform, but stopped short of calling on him to step down.

"From our perspective, he has lost legitimacy," Clinton told reporters at the State Department in a joint news conference with European Union foreign policy chief Catherine Ashton. "He has failed to deliver on promises he has made, he has sought and accepted aid from the Iranians as to how to repress his own people."

Congressional Republicans have pressed the administration to withdraw Ford from Syria, an ally of Iran that supports the Islamic militant groups Hezbollah in neighboring Lebanon and Hamas in the Gaza Strip. The US did not send an ambassador to Damascus for five years in protest of Syria's alleged role in the assassination of former Lebanese Prime Minister Rafik Hariri in Beirut.

Monday's protests coincided with government-organized talks in Damascus on possible political reforms after four months of unrest. But the talks were boycotted by the main opposition factions and are unlikely to produce any breakthroughs to immediately end bloodshed.

The two days of meetings, however, were seen as a major concession by Assad's regime after the most serious challenge to its rule.

The talks did not stop Syrian forces from pressing their crackdown.

Before the embassy attacks, Syrian troops stormed the country's third-largest city of Homs with armored personnel carriers and heavy machine guns, a rights activist. At least two people were killed and 20 wounded, activists said.

Activists including the Local Coordination Committees, a group that tracks anti-government protests in Syria, also reported gunfire and a "massive wave" of arrests and raids in the Jabal al-Zawiya region in Idlib province, near the Turkish border.

Clashes between protesters and Assad's supporters have resulted in the deaths of 1,600, in addition to 350 members of the security forces. Syria blames what it calls "armed gangs" and Muslim extremists for the violence.