Syrian security forces killed at least 17 protesters Wednesday and the U.S. ambassador’s car was attacked in Damascus today by government supporters.

Ambassador Robert Ford, a critic of President Bashar al- Assad, was stranded in the office of opposition lawyer Hasan Abdul-Azim when government supporters surrounded it, Mahmoud Merhi, head of the Arab Organization for Human Rights, said by phone today. The incident came as the United Nations Security Council prepares to debate a resolution condemning Syrian violence against protesters.

Ford escaped unharmed though his car was damaged after it was pelted with rocks, eggs and sticks, a person familiar with the situation said. The four-wheel-drive vehicle had dents and some of its windows were cracked or shattered, the person said.

Security forces killed protesters Wednesday in the central governorate of Homs, the northern province of Idlib and southern area of Daraa, Merhi said.

The protests in Syria are part of the wave of unrest across the Middle East and North Africa that unseated governments in Tunisia, Egypt and Libya. Assad’s crackdown has left more than 3,600 civilians dead since the unrest began in March, according to Ammar Qurabi of the National Organization for Human Rights in Syria. About 30,000 people have been detained and 13,000 are still being held, according to Qurabi and Merhi.

There have been reports in the last three days of clashes between security forces and Syrians who have defected from them, Merhi said. Al Arabiya television broadcast video today of army defectors saying they had attacked and killed agents of the government and freed 27 children and their teacher. Merhi said he could not verify if the statements were true.

Mark Toner, the U.S. State Department spokesman, said at a Monday briefing that it was a “natural development” that Syrian opposition groups would start using violence against security forces as an “act of self-preservation,” and that the responsibility for such violent acts lay with Assad’s government and its crackdown on dissent.

Syria’s foreign ministry said Toner’s comments were “irresponsible” and encouraged acts terror and chaos, the state-run Syrian Arab News Agency reported today. “The U.S. is involved in encouraging armed groups to practice violence” against the army, it said.

The Security Council is due to debate today what will be the third version of a European draft resolution, with a vote possible as early as tomorrow. Diplomats from Security Council members said they are optimistic agreement can be reached, after European countries agreed to ease demands for sanctions that had been opposed by Russia and China.