Nigeria's army said Tuesday it had liberated 30 hostages held by Boko Haram, including 21 children and seven women, amid ongoing offensives against the extremists in the country's northeast.

Army officials said the operation to free the captives took place in the town of Dikwa in Borno State, which had fallen to Boko Haram twice since April, and was recaptured by Nigerian troops last week.

"As a result of ongoing operations under the aegis of Operation Lafiya Dole to clear Dikwa and its environs from Boko Haram... (the) Nigerian Army yesterday rescued 30 persons from the hands of the terrorists," army spokesman Sani Usman said in a statement.

"They include 21 children and a six-day-old infant, seven women including three nursing mothers, and two elderly male adults," he said.

Dikwa is located around 90 kilometres (56 miles) east of Borno state capital Maiduguri.

Earlier Tuesday, 11 Boko Haram militants were killed in clashes with the military in a village in southern Borno state, a local resident and a member of the militia fighting alongside the army said.

Three militia fighters were also killed in the battle.

"On Monday afternoon around 2:00 pm (1300 GMT), Boko Haram gunmen on motorcycles attacked our village," said Markus Yohana, a local militia member fighting the Islamists in the village of Dille.

Yohana said that soldiers ambushed the raiders as they tried to flee, killing 11.

Another local, Bitrus Damina, confirmed the account.

"Soldiers went after them and killed 11 of them in the bush," Damina said.

Boko Haram has stepped up its attacks since Nigeria's new president Muhammadu Buhari was sworn in May.

The wave of violence has claimed 830 lives in just two months, dealing a setback to a four-country offensive launched in February that had chalked up a number of victories against the jihadists.

On Tuesday, Nigeria's military spokesman told AFP a new regional force tasked with fighting the jihadists will go into action soon.

The 8,700-strong Multi-National Joint Task Force, drawing in Nigeria, Niger, Chad, Cameroon and Benin, is expected to be more effective than the current alliance in the battle to end Boko Haram's six-year insurgency that has claimed some 15,000 lives.

"Any moment from now, the operations or the Task Force will be manifest. In other words, we may not tell you (when it will commence), you will just see it," Nigeria's military spokesman Major General Chris Olukolade told AFP, who declined to give further details for strategic reasons.

The force will have its headquarters in Chad's capital N'Djamena. A Chadian military source said offices had been set up in an army camp there for the new force's chief of staff.