Activists say Syrian government forces have used helicopter gunships to battle rebels in the capital Damascus.

The activists say that helicopters fired heavy machine guns during overnight clashes in the neighborhoods of Qadam and Hajar al-Aswad.

They say Damascus has been relatively quiet since 8 a.m. Tuesday after three days of intense clashes between troops and rebels.

The fighting has been the most sustained and widespread in the capital since the start of the uprising against President Bashar Assad 16 months ago.

The Britain-based Syrian Observatory for Human Rights and Damascus-based activist Maath al-Shami said the fighting concentrated in Kfar Souseh, Nahr Aisha, Midan and Qadam.

Syria's state-run news agency said Tuesday troops are still chasing "terrorist elements" who fled from Nahr Aisha to Midan.

UN leader Ban Ki-moon was headed to China on Tuesday amid alarm over the spiraling violence in Syria and a diplomatic push to get Russia and China to back a tougher response to attacks by the Assad regime.

Ban's trip comes ahead of a UN Security Council vote this week on whether to allow sanctions and military intervention in Syria if Assad's regime or insurgent forces fail to comply with a UN peace plan. Russia and China have blocked previous efforts to sanction Syria.