Syrian opposition activists say they have shot down a military helicopter over the capital, Damascus.
The Free Syrian Army said the aircraft had been firing at people in the north-eastern district of Jobar, and that it had crashed in neighboring Qabun.
State television confirmed that a helicopter had come down in Qabun.
On Sunday, opposition activists said government forces had massacred more than 300 people during their assault on the south-western suburb of Darayya.
Video footage and photographs have emerged, showing scores of bodies, including those of women and children.
State media blamed the opposition for the killings and said Darayya had been “cleansed of terrorist remnants”.
The chairman of the UN Human Rights Council’s Independent Commission of Inquiry on Syria, Paulo Pinheiro, said the killings might constitute a war crime.
According to opposition activists, the military helicopter was shot down as it was bombarding Jobar, as heavy fighting broke out between rebels and government forces.
Witnesses told the Reuters news agency the helicopter burst into flames after being hit by a projectile during an exchange of fire and crashed in a narrow residential street in Qabun.
“It was flying overhead the eastern part of the city and firing all morning. The rebels had been trying to hit it for about an hour, and finally they did,” said Abu Bakr, a local activist.
Activists posted video footage online which appears to show a burning helicopter crashing to the ground. Rebels can be heard shouting: “Allahu Akbar (God is greatest).”
State TV confirmed that a helicopter had crashed near the al-Ghufran mosque in Qabun, though it did not say if it had been shot down.
A spokesman for the FSA’s Badr Battalion in Damascus, Omar al-Qabuni, told the AFP news agency that the body of the pilot had been found.
“It was in revenge for the Darayya massacre,” he added.
The FSA also claimed to have shot down a Mig-23 fighter jet on 13 August in the eastern province of Deir al-Zour.
The helicopter appears to have been taking part in an increasingly fierce attempt by government forces to regain control of the capital’s suburbs, and heavy clashes are said to have erupted after it came down.
On Sunday, military helicopters were firing rockets at Jobar and the neighboring districts of Zamalka and Irbin, activists said.
Meanwhile, President Bashar al-Assad has reiterated his claim that a “foreign” conspiracy is behind the uprising in Syria and promised that he would not allow it to succeed “whatever the price might be”.
“What is happening right now is not just a plot directed against Syria but the region as a whole, of which Syria is a foundational stone,” he was quoted as saying by the state news agency, Sana.