The pro-regime Al-Watan newspaper confirmed the killing.

General Aziz Asbar was killed late Saturday along with his driver in the central province of Hama, the Syrian Observatory for Human Rights monitor said.

Asbar headed the research centre in Hama's Masyaf, which was targeted in Israeli air strikes last month and in September last year, the Britain-based Observatory said.

According to the United States sarin gas was being developed at the centre, a claim denied by Syrian authorities who say the country does not possess any chemical weapons after a 2013 agreement to hand over its chemical arsenal.

Observatory head Rami Abdel Rahman said that experts from regime ally Iran were present at the Masyaf centre, which was developing short-range surface-to-surface missiles.

"The general was close to Syrian President Bashar al-Assad and to Iran," the monitor said.

Al-Watan reported in its online version: "Doctor Aziz Asbar, head of the scientific research centre in Masyaf, has been killed after an explosion targeted his car in the Hama countryside."

An Israeli air strike targeted the centre on July 22, Syrian state media and the Observatory said. At the time an Israeli military spokesman declined to comment on the report.

A strike in September 2017 caused material damage at the centre, according to the Observatory which said a fire broke out at a weapons warehouse where missiles were being stored.

Israel has carried out numerous raids inside Syria since 2017, according to the Observatory, targeting regime forces and their allies from Iran and Lebanese movement Hezbollah.

More than 350,000 people have been killed and millions displaced since the start of Syria's civil war in 2011.