Western strikes early Saturday hit Syrian military bases and chemical research centres in and around the capital, a monitor said, as the US announced a joint operation against the Damascus government.

"The Western coalition strikes targeted scientific research centres, several military bases, and the bases of the Republican Guard and Fourth Division in the capital Damascus and around it," said the Britain-based Syrian Observatory for Human Rights.

The US, France, and Britain announced a joint operation against Syria's government, a week after a suspected chemical attack outside the capital Damascus left more than 40 people dead. 

The world leaders announced that the strikes targeted positions linked to the chemical weapons facilities of the Syrian government.

Moments after the announcement, loud blasts could be heard from the capital and large plumes of smoke emerged from its northern and eastern edges.

Syrian state media reported the joint operation and said there was preliminary information that a research centre northeast of the capital had been hit.

The US and Europe have both slapped sanctions on the Syrian Scientific Studied and Research Centre for its links to chemical weapons production in Syria. (AFP)