BEIRUT (REUTERS) - Fighters from the militant Islamic State in Iraq and Syria (ISIS) wrested areas of the north-eastern Syrian city of Hasaka from government control in fighting overnight, the Syrian Observatory for Human Rights monitoring organisation said on Thursday.

But a Syrian military source denied the report, saying the army had repelled the attack.

The city of Hasaka is divided into zones controlled separately by the Damascus government and a Kurdish administration whose well-organised militia has been on the offensive against ISIS, making significant gains against the group in its stronghold of Raqqa province.