Syrian government planes have attacked a busy market in a rebel-held suburb of Damascus, killing at least 82 people and wounding more than 200, activists said.
The raid in the capital was one of the deadliest single incidents involving government air strikes since the crisis began nearly five years ago.
Government air raids on rebel-held areas throughout the country have killed thousands over the past few years.
The air raids on the market in Douma occurred during rush hour when people were out shopping on the first working day of the week in Syria, the activists said.
"This is an official massacre that was carried out deliberately," said Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights. He said planes fired the first missile and minutes later when people gathered in the aftermath, another missile hit the same area.
Mr Abdurrahman, whose group has a network of activists around the country, said four missiles were fired on the market, killing 82 and wounding more than 200.
He said the death toll is expected to rise because many of the wounded are in critical condition.
The Local Co-ordination Committees, another activist group, said the air raids killed at least 100 and wounded about 300, adding that rescue workers were digging through the rubble in search of survivors.
"The situation is catastrophic," a Douma-based activist who goes by the name of Mazen al-Shami said. He added that clinics in the area were full and many of the wounded were being taken in civilian cars to other medical facilities as ambulances are overwhelmed.
Mr al-Shami said mosque loudspeakers were issuing calls for residents to donate all types of blood. He added that hundreds of people were in the busy market when the first missile struck the area, inflicting heavy casualties.
An amateur video posted online by activists apparently showed 40 bodies of men and boys lined on the side of a street as more bodies were being brought in. Another video showed people helping the wounded leave the heavily damaged market area.
Syria's civil war, now in its fifth year, has killed more than 250,000 people and wounded at least a million.
Yesterday, al Qaida's affiliate in Syria released seven members of a US-backed rebel faction that it abducted late last month, the rebel group said in a statement.
The Division 30 rebel group said in its statement that it hopes the Nusra Front will release the group's commander who has been held since July 30. Days after the abduction, the Nusra Front attacked the Division 30 command in northern Syria, leading to the near-collapse of the group that has dozens of fighters.