The London-based Syrian Observatory for Human Rights said that at least 68 barrel bombs were dropped on Daraya on Friday as agencies delivered food rations to the city on the brink of starvation.
This comes as the United States is leading airstrikes targeting ISIS extremists. The regime is bombing cities and towns trying to break away from government control, including the very groups armed by the United States to fight ISIS.
The bombardment and fresh twin suicide attacks on Saturday are chilling reminders of the lack of progress in the conflict, which has raged now for almost five years, causing hundreds of thousands of deaths, the destruction of towns and mass displacements.
At least 20 people were killed, including 13 civilians, and more than 30 people were wounded in twin suicide bombings outside the Shiite shrine of the Sayyida Zeinab in suburban Damascus area, according to the UK-based Syrian Observatory for Human Rights.
The first was carried out by a man wearing a suicide vest, and the second by a car rigged with explosives, the monitor said.
After mounting international pressure, President Bashar al-Assad's regime finally eased restrictions on aid deliveries to beseiged areas, including Daraya, which has essentially been cut off from normal food and water supplies since 2012 as the government tries to regain control of the opposition stronghold.
Assad's regime swiftly drew fierce criticism from abroad over the attacks.
"Obviously, such attacks are unacceptable in any circumstance; but in this case, they also hamper the delivery and distribution of badly needed assistance," U.S. State Department deputy spokesperson Mark Toner said in a press briefing Friday.
"It shouldn't be a situation where the Syrian government, for example, decides which areas receive humanitarian assistance," he added.
UK International Development Secretary Justine Greening welcomed the "arrival of desperately needed food supplies, delivered by UK-funded agencies" and she said Assad must "make good on his promise to let aid flow."
"At the same time, punishing areas where access has been agreed - whether attacks on children's hospitals in Aleppo or renewed barrel bombing on Daraya -- is utterly despicable and a violation of international humanitarian law," she said.
In Daraya, the local opposition council described "violent and concentrated bombing" by regime forces, causing "enormous devastation" to residential and farmland areas.
The U.N.'s World Food Program said it had delivered enough family rations of rice, lentils, chickpeas, beans, bulgur, oil, salt and sugar to feed 2,400 people for a month in Daraya. It also delivered flour in bags to feed the population of 4,000 people for a month. Other figures used by the council, however, show the population to be closer to 8,000.
The nine-truck convoy also delivered medical supplies and health items late Thursday to the city, and had left by early Friday morning.
The Syrian branch of the U.N.'s Office for the Coordination of Humanitarian Affairs called for the regime to end the siege.
A report from a handful of humanitarian agencies last year concluded that the world is failing the people of Syria.
This year a partial truce was reached, paving the way for the delivery of some aid into parts of the country that desperately needed it.
However, the so-called "cessation of hostilities" has significantly disintegrated, in turn making humanitarian assistance delivery more difficult.
The opposition's chief negotiator, Mohammad Alloush, resigned this month the failure of the peace talks, saying the international community had failed to stop the Assad regime's atrocities.