ISLAMIC State group jihadists, emboldened by a string of battlefield victories, have advanced to the gates of the Syrian city of Hasakeh after intense fighting with regime troops.

The jihadists have advanced to “500 metres away from the entrance of Hasakeh, after fierce clashes against regime forces south of the city,” said Rami Abdul Rahman, director of Britain-based monitoring group the Syrian Observatory for Human Rights.

He said IS had seized all military posts in that area of north-eastern Syria, including an unfinished prison building and a power plant, after at least six suicide bombers struck on Wednesday.

Regime helicopters, meanwhile, dropped barrel bombs on jihadist positions, he said.

Control of Hasakeh city is split between regime and Kurdish forces, who have fought IS elsewhere in the province.

If IS seizes Hasakeh it would be the second Syrian provincial capital to fall under its control, after Raqa, the group’s bastion in northern Syria.

Iran and Iraq have deployed thousands of fighters in Syria to help the regime defend Damascus and its surroundings, a security source told AFP on Wednesday.

“Around 7000 Iranian and Iraqi fighters have arrived in Syria over the past few weeks and their first priority is the defence of the capital. The larger contingent is Iraqi,” the source said on condition of anonymity.

Fighting on Wednesday around Hasakeh left 27 regime fighters and 26 jihadists dead, according to the Observatory, which relies on a network of sources on the ground.

The Al-Watan newspaper, which is close to the government, said IS had begun a “violent attack on Hasakeh” but criticised Kurdish forces for failing to support regime troops.