The damaged front side of the U.S. embassy is seen after pro-government protesters attacked the embassy compound in Damascus, Syria, Monday, July 11, 2011. The damage caused when a mob breached the wall of the compound before being dispersed by Marine guards. (STR/AP)

Secretary of State Hillary Rodham Clinton said Syrian President Bashar al-Assad has lost the legitimacy to rule after pro-government demonstrators stormed the U.S. Embassy in Damascus on Monday in what U.S. officials described as an orchestrated attack.

Regime supporters hurled rocks, smashed windows and tore down the American flag at the embassy, triggering the strongest U.S. condemnation yet of the Syrian government. Clinton suggested that the United States is contemplating the prospect of a post-Assad future in Syria nearly four months into a brutal government crackdown on pro-democracy activists inspired by the revolts in Egypt and Tunisia.

“From our perspective, he has lost legitimacy,” she said, marking the first time the United States has called into question the validity of the Syrian president. Syrian officials would be mistaken, she said, in concluding that repeated U.S. calls for democratic reforms in Syria signaled a desire to see Assad continue his rule — a conclusion many Syrians have reached.

“President Assad is not indispensable, and we have absolutely nothing invested in him remaining in power,” she told reporters at the State Department.

Her comments drew a stringent Syrian response on Tuesday, with Syria’s official news agency warning the U.S. to “refrain from any acts that could provoke the Syrian people’s emotions and pride in their national independence.”

The embassy attack also highlighted the vulnerability of American diplomats in the Syrian capital as well as the limits of U.S. statecraft at a time when tensions are soaring between the two countries over Syria’s treatment of protesters pressing for regime change.

Syria and the United States have had stormy relations dating to the 1950s, with occasional interludes during which the countries cooperated on counterterrorism investigations. In 2005, George W. Bush’s administration recalled the U.S. ambassador to Damascus over allegations that Syria was tied to the assassination of former Lebanese prime minister Rafiq al-Hariri.

The appointment of Robert Ford as the U.S. ambassador last year marked the first time since 2005 that the United States had filled the post, part of the Obama administration’s effort to repair relations with Syria.

Monday’s violence erupted after several hundred demonstrators waving portraits of Assad converged on the U.S. and French embassies in the morning to protest the visits on Friday by the American and French ambassadors to the Syrian town of Hama. The ambassadors had gone there to lend support to one of the largest anti-government demonstrations since the uprising began.

The assaults on the embassies also followed a blistering attack by Ford against the Syrian government, which he delivered, unusually, on Facebook. In his posting, he railed against the harsh tactics used by Syrian security forces to restrain pro-democracy demonstrations even as they allow anti-American rallies to go ahead.

U.S. officials said they would seek compensation for damage to the embassy in the latest attack, the most violent of several recent incidents there.

According to one State Department official, the demonstrations were staged after a program broadcast Sunday night on the private pro-government al-Dunia television network, owned by Rami Makhlouf, Assad’s tycoon cousin. In the program, Syrians were urged to express their anger at the ambassadors’ visits to Hama.

“It seems to be something people were encouraged to do,” said the official, who spoke on the condition of anonymity because of the sensitivity of the subject.

A U.S. Embassy official, who was not authorized to discuss the subject and spoke on the condition of anonymity, said that protesters arrived in buses and that Syrian security forces normally assigned to guard the perimeter of the embassy compound were slow to respond to U.S. appeals for help. In the meantime, about 10 demonstrators broke into the compound, destroying the main entrance, and three of them climbed onto the roof.

Once the protesters were inside the grounds, U.S. Marines confronted them, forcing them to flee. No protesters entered the embassy building.

“It was evident that the Syrian government orchestrated it using buses to transport and deliver the protesters,” the embassy official said, adding that Syrian security forces took at least an hour to disperse the crowd.

By late Monday, Syrian officials had not commented publicly on the allegations.

No embassy staffers were injured, and diplomats remained in the building throughout the hour-long onslaught, during which Syrian security forces made little effort to restrain the crowd, the State Department official said. “They basically stood by and let people do what they wanted,” he said.

The attack on the French Embassy, a few blocks away, seemed to be even more violent. The protesters not only hurled rocks and tomatoes, but also destroyed an embassy vehicle and used a battering ram to try to break through a garage door.

Guards inside the embassy opened fire over the heads of the protesters to try to disperse them. French officials said three embassy guards were wounded in the melee.

The attack occurred “under the watchful eyes of Syrian security forces who were clearly not in a hurry to halt the violence,” the French Foreign Ministry said in a statement.

Hours later, small groups of demonstrators were still milling around the two embassies, wrapped in Syrian flags and carrying posters of Assad as government security forces looked on. Some protesters also were waving the emblem of the Lebanese Shiite Hezbollah movement.

“We want the U.S. and the French to go out of Syria,” said one of the men, Mohieddin Jaafar. “And all Syrians love Bashar al-Assad.”

Graffiti referring to Ford as a “dog” and using expletives against the United States were scrawled on the walls of the U.S. Embassy. The bulletproof glass at the embassy’s entrance was smashed. Rocks lay strewn on the ground, and three Syrian flags fluttered from the high fence surrounding the embassy building.

U.S. officials acknowledged that the attack had exposed flaws in security at the embassy, which is beside a busy traffic circle and protected only by a fence, making it one of the most lightly guarded U.S. diplomatic missions in the world.

“We’re obviously looking at other measures that we can take to beef up security,” said State Department spokeswoman Victoria Nuland.

There was no suggestion to remove Ford from his post, however. Despite repeated criticism over the past few months, the State Department has opted to keep Ford in place, saying that his presence in Damascus and easy access to Syrian officials is of greater value than the symbolic gesture of recalling the ambassador to Washington.

Nuland rejected Syrian allegations that Ford had incited violent attacks on the embassy with his decision to travel last week to Hama.

Some members of the Syrian opposition have accused the United States of being slow to condemn the harsh tactics used by the government in its efforts to crush the rebellion. At least 1,300 people have died in the uprising, and many thousands have been detained.

But Sunday, Ford sharply escalated U.S. criticisms of the Syrian regime with his Facebook posting. Referring to less-violent anti-U.S. demonstrations that have taken place in recent days, Ford proposed that protesters donate to the poor the tomatoes and eggs that had been thrown at the embassy.

“And how ironic that the Syrian Government lets an anti-U.S. demonstration proceed freely while their security thugs beat down olive branch-carrying peaceful protesters elsewhere,” he added.

Warrick reported from Washington. Correspondent Ernesto Londono in Djerba, Tunisia, contributed to this report.