The Syrian Observatory for Human Rights said air strikes hit two towns in the eastern Ghouta enclave on Tuesday despite a Russian-ordered truce, but a Syrian military source denied this.
The U.K.-based monitoring group said helicopters dropped two bombs on the town of Shifouniyeh and a warplane struck the town of Aftaris. The military source denied the report.
The Russian military on Tuesday accused opposition groups in eastern Ghouta of raining mortar fire down on an evacuation route opened to allow civilians to leave the conflict zone, the TASS news agency reported.
Not a single civilian had been able to leave the area via the corridor as a result, TASS cited the Russian military as saying.
Russia, which backs the Syrian government, ordered a daily truce from 9 a.m. to 2 p.m. (0700 GMT to 1200 GMT) and the creation of a "humanitarian corridor" to let civilians leave the area, the last major rebel stronghold near Damascus.
Opposition groups denied responsibility for the attacks.
"We have not prevented anyone and civilians make their own decisions," said Yasser Delwan, head of the local political office of the Jaish al-Islam faction.
A journalist on the ground from Syria's state-run Al-Ikhbariya TV also said mortar shells had targeted the crossing, preventing civilians from leaving. It was not immediately possible to verify the claim.
Al-Ikhbariya broadcast footage from a crossing point manned by the Syrian military between the enclave, known as eastern Ghouta, and Damascus, saying preparations were underway to allow civilians to leave, including medical care. The TV said a restaurant was also set up there.
The Wafideen crossing point is near Douma, one of the largest towns in eastern Ghouta, only a few kilometers (miles) from Damascus. The TV showed small buses waiting at a parking area but there were no signs of anyone coming out of the enclave.
The Russian five-hour humanitarian pause, ordered by President Vladimir Putin, comes as a U.N. cease-fire failed to take hold in eastern Ghouta, and residents and aid groups said such unilateral pauses are not internationally monitored.
The enclave's residents fear they could face harassment and possibly arrest if they go into government areas, after years of living in the opposition-held enclave.
Ingy Sedky, spokeswoman for the International Committee of the Red Cross, said humanitarian corridors need to be well planned and must be implemented with the consent of parties on all sides.
"This is essential so that people can leave safely, if they chose to do so," she said. "And for those who decide to leave, all measure should be taken to provide assistance, protection and shelter to them. And those who remain must be protected from any attacks."
A weekend resolution unanimously approved by the U.N. Security Council for a 30-day cease-fire across Syria failed to stop the carnage in eastern Ghouta where more than 500 people have been killed since last week.
At least 34 people were killed on Monday by airstrikes and shelling, according to the Syrian Observatory for Human Rights. The U.N. estimates that nearly 400,000 people live in dire conditions from the siege in eastern Ghouta, which has been under intensive bombing by government forces for weeks.
Rami Aburrahman of the Syrian Observatory for Human Rights said violence has dramatically declined in eastern Ghouta overnight but reported a number of shells on Tuesday morning. It was not immediately clear where they landed or who fired them, Abdurrahman said.
Firas Abdullah, a Douma activist, said a bomb landed in the town after the pause began, as well as three ground missiles.
Civilians caught in the violence have mocked Putin's order of a five-hour open corridor, saying it gives only a couple of hours of calm before violence resumes.
Russia's military campaign to support Syrian President Bashar Assad has helped turned the tide of the war in the Syrian government's favor.
The eastern Ghouta residents also fear their region would meet the same fate as the eastern, rebel-held half of the city of Aleppo, where a similar Russian-ordered pause in 2016 called on residents to evacuate the area and for gunmen to lay down their arms.
A full ground assault followed, finally bringing Aleppo under government control.