Crowds of Syrians loyal to President Bashar al-Assad surged into the U.S. embassy compound in Damascus on Monday and caused damage.

The Associated Press reported that attackers broke windows, raised a Syrian flag on the U.S. grounds, and wrote anti-U.S. graffiti on walls. The attackers reportedly left after the brief incursion.

Reuters news agency quotes an unidentified U.S. official as saying the Syrian security response to the assault was “slow and insufficient.” U.S. officials said they will summon a senior Syrian diplomat in Washington to protest the attack.

The assault on the embassy comes amid rising tension between the Obama administration and Syria's government, after last week's visit by the U.S. ambassador to the flashpoint city of Hama.

Ambassador Robert Ford and French Ambassador Eric Chevallier traveled to Hama Thursday and Friday to show solidarity with its residents, who have come under attack from government forces while staging some of the largest protests to date against Mr. Assad.

The United States on Sunday accused Syria of organizing a two-day demonstration outside the U.S. embassy in Damascus to protest the ambassador's visit to besieged Hama. France lodged similar complaints Sunday after a pro-government mob damaged its Syria missions.

Syria's foreign ministry called the visits “flagrant interference” in the country's internal affairs meant to undermine its stability.

Meanwhile on Monday, rights activists and residents say Syrian troops backed by armored vehicles entered the central city of Homs, killing at least one person and wounding 20 others.

The actions come as Syria holds the second day of what it calls a national dialogue on political reform.

Some government critics have joined the talks in Damascus, but the main opposition groups are boycotting to protest President Assad's deadly crackdown on the anti-government uprising.

During the first day of talks Sunday, a number of speakers condemned the security forces and violence against protesters. But others repeated Mr. Assad's contention that foreign agitators are trying to destabilize Syria.

Mr. Assad proposed the dialogue last month as a gesture to the opposition, which has been holding regular mass protests since March to demand an end to his family's four-decade rule of the country.

Rights groups say Syrian security forces have killed at least 1,600 civilians during the crackdown, while the government blames the violence on terrorists and Islamists who it says have killed hundreds of security personnel.