Fresh shelling of Eastern Ghouta endangered a vital aid delivery on Friday, nearly three weeks into a blistering Syrian regime offensive that has seized more than half of the rebel enclave.
More than 940 civilians have been killed since Russia-backed government forces launched an assault on the last opposition bastion near Damascus on February 18.
A charity called for desperately needed medical supplies to be allowed into the enclave, where exhausted doctors and nurses have been struggling to treat hundreds of wounded with very little equipment.
Early Friday, the air strikes stopped briefly, with the area seeing its calmest night in more than a week, according to the Britain-based Syrian Observatory for Human Rights monitoring group.
Taking advantage of the relative quiet, 13 trucks loaded with 2,400 food parcels entered Eastern Ghouta on Friday morning, the International Committee of the Red Cross said.
But air strikes and shelling resumed near the enclave's main town of Douma after the trucks from the joint ICRC, Syrian Arab Red Crescent and United Nations convoy drove in.
"Shelling in proximity of Douma, east Ghouta today, is putting the UN/ICRC/SARC convoy at risk, despite assurances of safety from parties including the Russian Federation," the UN humanitarian coordinator in Syria, Ali al-Zaatari, said in a statement.
"The UN calls for a cessation of hostilities in the area and for calm throughout Syria so that aid can be safely delivered to people in need," Zaatari said.
'Hopelessness and despair'
There were no medical supplies on board Friday's convoy, which was carrying food that aid workers were unable to distribute on Monday.
The enclave's 400,000 inhabitants have been living under government siege since 2013, with food and medicines in very short supply even before the latest assault.
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.
Syrian state news agency SANA said dozens of civilians were expected to leave Eastern Ghouta on Friday.
The air and ground assault has left exhausted medical staff struggling to cope with hundreds of wounded civilians pouring in to hospitals covered in blood and dust.
Doctors and nurses in the beleaguered enclave have run out of several life-saving items and a massive medical re-supply is critically urgent, Doctors Without Borders (MSF) said Friday.
"The need for a massive medical re-supply, without life-saving items being removed, is increasingly urgent with each passing hour," MSF said in a statement.
The Paris-based charity urged the warring parties to pause the bombing and shelling to allow for the evacuation of critically sick or wounded patients.
More than a week ago, the United Nations said those already numbered more than 700.
MSF said doctors inside the enclave were exhausted.
"Daily, we hear of an increasing sense of hopelessness and despair, as our medical colleagues reach the limits of what a person can be expected to do," MSF director general Meinie Nicolai said.
The charity said 15 of the 20 medical facilities it supports in Eastern Ghouta have been hit by air strikes or shelling.
Regime forces have advanced rapidly through farmland in the enclave since last week, according to the Observatory, taking control of more than half of the territory from the armed opposition.
They are now seeking to cut off Douma from rebel-held territory further south, Observatory head Rami Abdel Rahman said.
On Monday, 46 trucks entered the area in the first aid provision since the new offensive against the enclave began on February 18 -- but they had to cut their deliveries short and leave due to heavy bombardment.
Nearly half of the food aid could not be delivered while the UN said Syrian authorities removed some medical and health supplies from the trucks.
More than 340,000 people have been killed since Syria's war started in 2011 with a brutal crackdown on anti-government protests.
Numerous rounds of UN-backed peace talks have failed to bring an end to the conflict, and a nationwide ceasefire called for by the UN Security Council last month has not been implemented.
The council is to meet on Monday to hear a report from UN Secretary General Antonio Guterres and try to plod on with a bid to turn the ceasefire voted in New York into a reality on the ground.