MAIDUGURI: Witnesses say two female suicide bombers killed 13 people at a crowded market and a military checkpoint in northeastern Nigeria.

It is the fourth attack this week in which more than 160 have been killed as Boko Haram Islamic extremists appear to follow an Islamic State group order to step up attacks in the holy month of Ramadan.

In the most deadly attack, the militants targeted several mosques in northeastern Kukawa town on Tuesday and gunned down nearly 100 praying worshippers.

Security guard Abba Shehu said Thursday's attacks began with an explosion from a teenage girl at Malari village market outside Maiduguri city. He said at least 10 people were killed.

Minutes later a woman in a taxi blew up at a military checkpoint, killing a soldier and two passengers.