Sirens ring out as air strikes hit Islamic State's Syria stronghold

Beirut: In the Islamic State group's Syrian stronghold of Raqa, sirens ring out whenever a warplane approaches as jihadists flee their posts and vehicles to hide, activists say.

A US-led coalition and Russia have stepped up air strikes on the jihadists' de facto Syrian capital since ISIS claimed to have downed a Russian passenger plane over Egypt's Sinai in October and the deadly jihadist attacks in Paris two weeks later.

"The sirens are on the roofs of high buildings, in the squares and in the streets," Taym Ramadan, a city resident and anti-ISIS activist, told AFP.

"When a warplane enters Raqa's air space, the sirens ring out to warn (ISIS) members," said the activist from the "Raqa is Being Slaughtered Silently" campaign group.