BEIRUT — Syrian rebels battled regime forces Monday in a heavily protected, upscale area of Damascus, activists said, in a sign that the country's outgunned opposition is increasingly turning to insurgent tactics.

At least three people were killed in the firefight, which was the most serious clash in the Syrian capital since the uprising began a year ago. The battle with machine guns and automatic rifles brought the country's violent conflict to the streets of a neighborhood that houses embassies and senior government officials.

The Britain-based Syrian Observatory for Human Rights, which has a network of activists throughout the country, said 18 government troops were wounded in the fighting and two later were believed to have died.

Rami Abdul-Rahman, who heads the Observatory, described the clash "as the most violent of its kind and closest to security centers in Damascus since the revolution began."

He said several "armed groups of defectors" came from one of the suburbs and fired a rocket-propelled grenade at the house of an army brigadier general. They then entered a building where they were chased by security forces.

It was not clear whether the general was hurt, he said.

The state-run SANA news agency gave a different version of events, saying the fighting broke out when security forces stormed an apartment used as a hideout by an "armed terrorist" group in the Mazzeh neighborhood.

The report said two gunmen were killed and a third was arrested while a member of the security forces was killed.

Due to restrictions on journalists in Syria, it was impossible to reconcile the two accounts. Since the start of the uprising against President Bashar Assad, the regime has referred to its opponents as terrorists and insisted the revolt is driven by a foreign conspiracy, not popular will.