Reports from Nigeria say members of the Boko Haram militant group are gathering in their stronghold of Gwoza and bringing in reinforcements from other locations.

An intelligence source who is monitoring the situation tells VOA that military forces are getting closer to the town and the militants may be preparing to defend Gwoza, which is one of the last major towns they control in northeastern Nigeria.

The source says Boko Haram reinforcements are traveling to Gwoza from their refuge in the nearby Sambisa forest.

Gwoza is located about 135 kilometers south of the Borno state capital, Maiduguri.

The Associated Press reports the militants are surrounding the town with land mines and warning civilians to flee. It says the fighters have released some young women they had been holding.

VOA's source says earlier this week, militants in Gwoza killed some civilians who refused to take up arms with Boko Haram to defend the town.

In the past month, Nigeria has reported success in retaking towns and villages from Boko Haram, including the Borno state town of Mafa on Thursday.

The offensive is being aided by forces from Niger, Cameroon and Chad, all of whom have suffered Boko Haram attacks on their territory.

Earlier this week, Chad said its forces had liberated the town of Dikwa. Chad's President Idriss Deby called on Boko Haram's chief Abubakar Shekau to surrender or be killed, saying his forces know Shekau's location.

On Thursday, it was reported that Boko Haram militants killed at least 68 people in a raid on the Borno state village of Njaba. A survivor of the attack told VOA that gunmen killed all the men and teenage boys in the town, including children as young as 12 years old.

Because of the remoteness of the area, word of the attack took two days to reach the state capital, Maiduguri, about 100 kilometers away.

Boko Haram is blamed for thousands of deaths in Nigeria since launching its insurgency in 2009. The group is purportedly fighting to establish an Islamic state in northeastern Nigeria.