Western powers have criticised President Bashar al-Assad's government, accusing its forces of dropping barrel bombs on the Syrian town of Daraya just hours after it received its first food aid in almost four years.
The military used the crude, unguided weapons known to kill indiscriminately multiple times on Friday.
A convoy of trucks carrying food arrived in Daraya late on Thursday, delivering rice, lentils, sugar, oil and wheat flour to civilians for the first time since the government laid siege to the town in late 2012.
Assad's forces bombarded the town shortly after the delivery, according to a witness and human rights monitors, dropping the barrel bombs from helicopters as residents shared food.
Shadi Matar, a local council member, said aid had not yet been distributed "because of the intensity of the raids".
Jean-Marc Ayrault, France's foreign minister, accused Syria of "extraordinary duplicity" over the bombings, which came just as aid workers were beginning to distribute supplies to thousands of people.
Ayrault said he was "outraged beyond words", declaring the end of an already shaky ceasefire and calling for world powers to meet.
Mark Toner, US state department spokesman, said "such attacks are unacceptable in any circumstance, but in this case they also hampered the delivery and distribution of badly needed assistance".
Matthew Rycroft, the UK's ambassador to the UN, described the bombing as "atrocious.
"The international community is united around the obligations of the Assad regime," he said.
Nearly 600,000 people live in besieged areas in Syria, most surrounded by government forces, and another four million in hard-to-reach areas, according to the UN.
Aid agencies said supplies also reached Douma on Friday - the first UN delivery since autumn 2013, according to the Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group.
The Syrian Arab Red Crescent said 39 trucks took food and non-food items including medicines into the besieged town.
But the UN's humanitarian agency was still awaiting Syria's approval to deliver aid to two more of Syria's besieged areas: Al-Waer in Homs province and Zabadani in rural Damascus.
UN-backed peace talks on ending Syria's civil war stalled in April when the opposition walked out over lack of humanitarian access.
The conflict has killed more than 280,000 people and displaced millions since it started in 2011 with the repression of anti-government protests.