The Syrian Observatory for Human Rights reported Monday that "Israeli warplanes" had launched strikes on military targets including "the Barzeh scientific research centre" and naval vessels and army warehouses in and around the Latakia military port.

The strikes came on the heels of the collapse of former president Bashar al-Assad's government over the weekend in the face of a lightning rebel advance.

Western countries including the United States had previously struck the research facility in Barzeh in 2018, saying it was related to Syria's "chemical weapons infrastructure".

On Tuesday, three blocks of buildings that made up the centre were completely destroyed, according to an AFP journalist at the scene, with fire still burning among the ruins.

Hundreds of documents were scattered on the ground, some on fire, as a strong smell of explosives lingered in the air.

An employee who worked at the centre for 25 years and came to inspect the damage said that "the buildings destroyed were not military".

"The military centres were destroyed in the past, and the current research was civilian," he added, requesting anonymity.

A "second scientific research centre", based in Jamraya near Damascus, was also hit by strikes Monday night and "totally destroyed", he said.

AFP journalists in Damascus heard heavy strikes overnight into Tuesday morning.

- Navy ships -

In Latakia, smoke was still rising Tuesday morning from the wreckage of navy ships equipped with machine guns and rocket launchers, half-sunk in the water, an AFP correspondent saw.

Ahmad Khabaze said civilian employees such as himself had not stopped coming to work at the sea port.

"Employees are still coming in to take care of state facilities even after the regime fell," he told AFP.

Another civilian port employee, Samir Alloush, 54, told AFP he heard "strange noises in the night that went on for so long".

The region of Latakia was the heartland of Assad's minority Alawite community, but after the rebel takeover, people there toppled a statue of the deposed dictator's father.

The Observatory reported more than 300 Israeli strikes across the country in the days since Assad fled, saying they had destroyed Syria's "most important military sites".

Israel has conducted hundreds of strikes on Syria since the civil war began in 2011 following Assad's crackdown on a democracy movement.

On Monday, Israel said it had struck "remaining chemical weapons or long-range missiles and rockets in order that they will not fall in the hands of extremists".