Inspector General Suleiman Abba told reporters that police would “not relent in the efforts of tracing them”.

Initially, police said 35 officers were missing after the attack on August 21. Abba said some had since returned, without explaining how.

“We have been able to trace some of the officers who have reported back to their bases. Some have even reported back to their families,” he said.

Boko Haram Islamists attacked the police academy near Gwoza in Borno state two weeks after they seized the town and declared it part of an Islamic caliphate they are seeking to establish in northern Nigeria.

They went on to capture Bama, 50 kilometres (30 miles) to the north on September 1, killing scores of people.

The government, which has faced criticism for its failure to effectively confront the militants, said on Tuesday it was fighting back successfully.

“Only this morning it was reported that the military is in total and firm control of Bama,” government spokesman Mike Omeri told reporters.

“Consistent effort is ongoing to ensure that firm control is taken of areas that are being challenged by insurgent actions.”

Boko Haram is blamed for more than 10,000 deaths since 2009 and has repeatedly targeted the police and military.

It is believed to be in control of large swathes of Borno, its historic stronghold, as well as towns and villages in neighbouring Adamawa and Yobe. The three states have been under emergency rule since May last year.