Islamic state captures key base from Syrian army: monitor group

Islamic State militants captured the key Brigade 93 Syrian army base in Raqqa province overnight, the Syrian Observatory for Human Rights said on Friday.

"The IS took Brigade 93 after fierce fighting and a triple suicide bomb attack," Observatory chief Rami Abdel Rahman said, adding that government forces now hold just one position in the province at Tabqa airport.

Some troops had already pulled out of Brigade 93 in July after IS captured Division 17, another base in the region where at least 85 people were killed in fighting or summarily executed shortly afterwards, the Britain-based Observatory said.

Since joining the conflict in Syria in spring 2013, IS has seized control of almost all of Raqqa and Deir Ezzor provinces on the border with Iraq, where it has waged a devastating offensive since June.

At the end of June, IS declared a caliphate in territory it controls in Syria and Iraq.

The Observatory estimates that more than 170,000 people have been killed in Syria since March 2011, the start of a peaceful uprising against President Bashar al-Assad's regime that developed into an armed revolt.