At least 30 Islamic State fighters were killed on Friday in US-led coalition air strikes around the eastern Syrian city of Raqqa, the Syrian Observatory for Human Rights monitoring group said.
Observatory head Rami Abdulrahman said the attacks targeted depots of military vehicles and tanks, training camps and a prison used by the group east and west of Raqqa, the largest Syrian city under Islamic State control.
"At least 30 are confirmed killed. This is one of the biggest attacks. It dealt a major blow to the group," Abdulrahman told Reuters. It was not immediately possible to independently verify the account.
Islamic State seized large areas in Syria and Iraq and declared a self-imposed Islamic caliphate last year but has come under strain after a series of defeats in Syria brought about in part by air strikes on its forces and infrastructure.
It was forced to withdraw from the Kurdish town of Kobani after four months of fierce fighting with Kurdish militia aided by US air support, and has lost ground to Syrian government and Kurdish forces elsewhere.