BEIRUT - Syrian government forces have sent reinforcements to an air base being attacked by Islamic State militants in northeast Syria where no fewer than 30 of the radical group's fighters were killed on Thursday, a group monitoring the violence said.

The airbase at Tabqa, some 40 km (25 miles) east of the city of Raqqa in northeast Syria, represents the government's last foothold in an area otherwise controlled by the Islamic State group that has seized swathes of territory in Syria and Iraq.

The Syrian Observatory for Human Rights, which says it gathers material from all sides in the Syrian conflict, said the reinforcements had been flown in overnight into Friday.

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