At least 58 people were killed in Syria on Sunday in Syrian government airstrikes on the rebel-held town of Douma near Damascus, a monitoring group said.
The attacks on a market wounded another 200 people, mainly civilians, according to the Britain-based Syrian Observatory for Human Rights.
"The preliminary information suggests most of the dead are civilians," head of the organization Rami Abdul Rahman said.
Opposition fighters in Douma have regularly traded fire with the Syrian military during the country's civil war, now in its fifth year.
The conflict has killed an estimated 250,000 people since it began in 2011.
The strikes come as U.N. humanitarian chief Stephen O'Brien visits the country for the first time since taking over the post in May.
"Beyond destruction of buildings lies destruction of lives," he posted to social media.
Also in Syria on Sunday, a U.S.-backed rebel group says an al-Qaida affiliate has released seven of its members abducted last month.
The al-Nusra Front kidnapped the men in late July, accusing them of serving American interests.
"We welcome this noble initiative and urge the brothers of Al-Nusra and hope that they will release in the coming hours the group's commander and other fighters," the rebel group said in an online statement.
The commander and several more members of the so-called Division 30 group remain in captivity.
The United States has trained a small group of moderate Syrian rebels to fight the Islamic State militants fighting for territory in much of the country.
Some material for this report came from AP, AFP and Reuters.