Fighting has continued in the rebel-held Eastern Ghouta area in Syria, despite a five-hour “pause” ordered by the government’s ally Russia.
Activists said the government carried out a number air and artillery strikes, while state media accused rebels of shelling a “humanitarian corridor” meant to allow civilians to leave.
As a result, there were no UN aid deliveries or medical evacuations.
Earlier, the US called on Russia to use its influence to secure a 30-day truce.
The UN Security Council unanimously passed a resolution demanding a nationwide cessation of hostilities on Saturday, but it did not give a specific start date.
A spokesman for the UN Office for the Co-ordination of Humanitarian Affairs (OCHA) said it had received reports that fighting continued after the Russian-ordered pause began on Tuesday morning.
“Clearly, the situation on the ground is not such that convoys can go in or medical evacuations can go out,” Jens Laerke told reporters in Geneva.
The Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group, said the situation in the Eastern Ghouta had been relatively calm overnight.
But it reported that in the first two hours of the Russian-ordered “humanitarian pause”, a number of shells hit the towns of Douma, Harasta and Misraba.
Later, it reported air strikes, including the dropping of two barrel bombs on the town of al-Shifuniya, and rocketfire in the enclave.
The Syrian Civil Defence, whose volunteer rescue workers are widely known as the White Helmets, said one person was killed in Douma by shellfire. But the Syrian Observatory said the attack happened before the pause began.
The Syrian state news agency, Sana, reported that “terrorists” had shelled the route of the humanitarian corridor leading to the government-controlled al-Wafideen Camp, which is north-east of Douma, and were using “human shields”.
At least 568 civilians have been killed in government air and artillery strikes on the enclave over the past nine days, according to the Syrian Observatory.
Russia said the pause in bombardment would run from 09:00 until 14:00 local time (07:00-12:00 GMT) daily.
The Syrian Red Crescent would help set up the humanitarian corridor and residents would be informed about how to leave via leaflets, text messages and videos, it added.
Buses and ambulances will be waiting at a crossing to evacuate the sick and wounded.
“Five hours is better than no hours, but we would like to see an end to all hostilities extended by 30 days, as stipulated by the Security Council,” UN spokesman Stephane Dujarric told AFP news agency.
Meanwhile, UK Foreign Secretary Boris Johnson said it should consider carrying out air strikes in Syria if there was evidence that chemical weapons had been used.
“If we know that it’s happened, and we can demonstrate it, and if there is a proposal for action where the UK could be useful, then I think we should seriously consider it,” he told the BBC.
His comments came two days after a reported chlorine attack on the Eastern Ghouta. The Syrian government has denied using chemical weapons, but UN experts are confident it has used chlorine and the nerve agent in Sarin in the past.