A "good number" of unmanned US military and intelligence drones are operating in the skies over Syria, monitoring the Syrian military's attacks against opposition forces and civilians, NBC News reported.

Citing unnamed US defense officials, the TV network said this surveillance was not in preparation for US military intervention.

However, the administration President Barack Obama hopes to use the overhead visual evidence and intercepts of Syrian government and military communications in an effort to make the case for a widespread international response, the report said.

NBC News said there has been some discussion among White House, State Deptartment and Pentagon officials about possible humanitarian missions in Syria.

But US officials fear those missions could not be carried out without endangering the people involved and would almost certainly draw the United States into a military role in Syria, the report noted.

At least 30 people were reported killed Friday as protests spread to several well-to-do neighbourhoods of the Syrian capital for the first time and security forces unleashed their heaviest pounding yet of the flashpoint central city of Homs.