At least 20 people were killed and 15 others injured when Syrian warplanes dropped vacuum bombs on busy residential areas in eastern Damascus on Sunday, according to opposition activists.

The attack in Douma neighborhood used five vacuum bombs that killed 20 people, including women and children, and injured 150 others, Syrian activist Youssef Al Bustani from the Syrian Revolution Coordinators’ Union said.

Vacuum bombs are a type of thermobaric weapons, which go off at high altitudes dispersing a cloud of fuel that triggers a second explosion.

“Many of the injured are in critical condition after two-days of intense Assad regime attacks in the area,” he said.

Syria has been gripped by fighting since the regime launched a violent crackdown in response to anti-government protests in March, 2011 triggering a conflict that has spiraled into a civil war.