A humanitarian convoy entered Syria's Eastern Ghouta during a lull in fighting on Friday but the delivery of aid was threatened by a resumption of shelling in the embattled rebel-held area near Damascus.
Damascus and its main ally Moscow have both said the assault is needed to stop rebel shelling of the nearby capital Damascus and end the rule of Islamist insurgents over civilians in eastern Ghouta.
A previous delivery of aid to the region was cut short amid shelling.
The 13-lorry convoy is expected to distribute the rest of the aid that was unable to be offloaded on Monday, when initial attempts were interrupted by government bombing on the besieged area, the International Committe for the Red Cross said.
Rebels deny this and say the area's inhabitants have not crossed into government territory because they fear persecution. The war monitor, the Syrian Observatory for Human Rights, on Friday gave a death toll of 931 civilians in the campaign.
ICRC spokeswoman Indy Sedky said the trucks crossed into eastern Ghouta "after getting security guarantees from all parties to make sure no incident will happen during the presence of our team" in the city.
Additional reporting from Newsy affiliate CNN. Once the relief workers arrived, Syrian government forces shelled the outskirts of the town, he said.
The renewed artillery fire came as representatives of Damascus and businessmen pressed negotiations on a solution that would allow civilians or fighters to leave the enclave, the Observatory said.
MSF collects its data from 20 medical facilities to which the organization provides full or partial support.
The government and its Russian backers, determined to wrest eastern Ghouta from rebel control after seven years of war, recently intensified the shelling and bombardment to clear the way for its troops to advance on the ground.
A top United Nations aid official is appealing to Russian Federation and the Syrian government and those who have influence over armed opposition groups for a cessation of hostilities in eastern Ghouta.
Almost 400,000 people are believed to be inside eastern Ghouta.
A tribal leader said more than 300 civilians from the areas of Kafr Batna, Saqba and Hammuriyeh wanted to leave.
On Monday, a convoy of 46 trucks delivered some provisions to Douma but was forced to turn back.
Local Syrians in parts of Damascus' East Ghouta pocket have been protesting against militants, calling on them to leave the area and allow the Syrian Army in.
Reports of malnourishment were also rampant and many of Eastern Ghouta's residents were living in poorly equipped basements for some respite from almost incessant shelling. "Some say I want to stay, some say I want to go but both options have become unsafe, this is what makes me so anguished", he said.
More than 100 people have been killed in the enclave in the past 48 hours, said Mr. Dujarric, adding that since 24 February, when the UN Security Council adopted a resolution demanding a cessation of hostilities throughout Syria, hundreds of people have reportedly been killed and thousands injured due to air and ground strikes.