Syrian government forces used deadly nerve gas in Khan Sheikhun and in three other recent attacks, Human Rights Watch said Monday, describing a “clear pattern” of chemical weapons use that could amount to crimes against humanity.

President Bashar al-Assad’s forces are also stepping up chlorine gas attacks and have begun using surface-fired rockets filled with chlorine in fighting near Damascus, the US-based rights group said in a new report.

“The government’s use of nerve agents is a deadly escalation — and part of a clear pattern,” said Kenneth Roth, Human Rights Watch’s executive director.

“In the last six months, the government has used warplanes, helicopters, and ground forces to deliver chlorine and sarin in Damascus, Hama, Idlib and Aleppo.” […]