Syrian forces ambushed and killed nine army deserters in a north Damascus suburb on Monday, May 21 a human rights watchdog said, as NATO ruled out military action against the regime of President Bashar al-Assad, AFP reported.

The bloodletting also appeared to spill over into neighbouring Lebanon where two people were killed overnight in street battles between pro- and anti-Syrian groups in Beirut, a security official said.

The latest violence in Syria comes after a rocket-propelled grenade exploded on Sunday near UN observers in a Damascus suburb, and at least 48 people were killed elsewhere in the country.

The nine army deserters were killed as they were retreating under cover of darkness from the village of Jisr al-Ab near Damascus's Douma suburb, said the Syrian Observatory for Human Rights.

The Britain-based watchdog on Sunday had reported fighting between rebels and regime troops near Douma, during which the RPG exploded near a team of UN military observers.

No one was hurt in the Douma blast, which came as UN mission head Major General Robert Mood and peacekeeping chief Herve Ladsous were leading observers around the north Damascus suburb.

Heavy fighting also raged overnight between soldiers and rebels in other parts of Damascus province, despite an April 12 truce brokered by envoy Kofi Annan that the UN observers are overseeing.

NATO, which undertook a major air war in Libya to back rebels who fought Moamer Kadhafi's forces last year, said it has "no intention" of taking military action against Assad's regime.