At least four Red Crescent aid workers have been injured in the besieged Syrian city of Homs, after coming under fire Saturday.

Pro- and anti-government sources have traded blame for the incident; Syrian state TV blamed "terrorist groups" for the attack, which included a barrage of mortar shells. The opposition Syrian Observatory for Human Rights, however, blamed regime forces.

On its Twitter account, the Red Crescent simply stated "shots fired targeting aid trucks and the team", and the an "aid truck driver (was) wounded", without blaming either side.

"Mortar shells falling in close proximity near the team and aid trucks that moved into Old City," it said in a second tweet.

UN aid workers have been trying to get desperately-needed supplies to some 3,000 civilians still trapped in the city, including food, water and medicines. The flashpoint city, which has been at the center of the nearly three-year uprising against the Assad regime, has been under siege for a year and half, as government forces attempt to retake control from a coalition of rebel brigades.

On Friday, a ceasefire was brokered to allow the remaining civilians to be evacuated. According to reports only around 80 women and children were able to leave before renewed clashes broke out.

Some residents told the BBC that bread had not been available for months, and that many people had resorted to eating weeds and leaves to survive. 

The threat of starvation hangs over hundreds of thousands of Syrians inside the country, amid reports that government forces are using starvation as a weapon to starve-out rebel-held areas.

The Syrian civil war is believed to have killed well over 115,000 people since it began in March 2011.