At least 35 Nigerian police officers deployed to a training academy in the northeast region have gone missing after a Boko Haram attack on the facility, a government spokesman has said.

The government admitted that the armed group attacked the academy just outside the town of Gwoza in Borno state earlier this week, Al Jazeera's Rawya Rageh, reporting from capital Abuja, said on Sunday.

Our correspondent, however, said that government authorities have refused to confirm whether the officers were killed in the raid, taken by Boko Haram, or had gone in hiding from the armed fighters.

"But this is consistent with attacks in the past," she said, citing the recent abductions in the restive region, including kidnapping of more than 300 school girls in the town of Chibok.

Boko Haram seized Gwoza earlier this month, but the military has said it was preparing an offensive to retake the town.

In a statement issued late on Saturday, police spokesman Emmanuel Ojukwu said that since the attack, there have been "very promising prospects" of locating the missing police officers.

Escalating violence

Ojukwu, however, said that some may have been killed, but that their bodies have not yet been found.

Boko Haram, blamed for more than 10,000 deaths since 2009, has repeatedly targeted the police and the military throughout an armed offensive aimed at creating a strict Islamic state in the north.

The crisis has intensified in recent months.

The armed group is believed to be in control of large swaths of territory in Borno, its historic stronghold, as well as at least one town in neighbouring Yobe state.

President Goodluck Jonathan declared a state of emergency in the northeast in May of last year, and the military launched a massive operation to flush out the rebel group, which showed some initial success.

But analysts say top brass failed to sustain the pressure, allowing Boko Haram to regroup and recapture a group of towns and key roads in the region.