Syrian government forces and rebels traded fire across Daraa

The activist-run Nabaa Media outlet released footage of thick black smoke rising over the city following a string of blasts. It alleged the government was using napalm-like weapons. The footage was filmed Sunday.

A Syrian army general in Damascus did not immediately respond to a request for comment.

Daraa is an important link on the highway connecting Damascus to Jordan and was once an important source of customs revenue for the capital. It has been contested between the government and the opposition since the first anti-government demonstrations in 2011.

Nabaa contributor Mohammad Abazeid said the city's opposition-held areas are "nearly empty" and have been heavily damaged by the bombardment.

Abazeid said some 20,000 residents have fled the opposition-held quarters of the city since February.

The government's attacks have been concentrated on Daraa's Old City and its Palestinian refugee camp, according to the Britain-based Syrian Observatory for Human Rights. It reported clashes between rebels and pro-government gunmen inside the camp, which is a built-up residential area.

An infant was killed in rebel shelling of the government-held parts of the city, according to the Observatory and Syrian state media.

A "de-escalation agreement" brokered by Iran, Russia and Turkey in May has not brought any relief for the city, activists said.

The agreement covers four zones in Syria where the rebels are fighting pro-government forces.

Syria is in the sixth year of a civil war that has killed more than 400,000 people.