Nigeria's police said on Saturday terrorists killed 17 officers last week in a raid at a special training centre in the country's northeast.

Since 2009, the West African country has been battling Boko Haram terrorist group and its splinter faction.

"The Nigeria Police Force regrettably announces the tragic loss of seventeen (17) police officers who paid the supreme price.... following a terrorist attack on the Nigerian Army Special Forces School," on May 8 said a statement from the force.

"The officers, who were undergoing specialised operational training at the institution, lost their lives when terrorists launched a coordinated attack on the facility from multiple directions at about 0115hrs (0015 GMT)," it said of the attack in northeastern Yobe state.

Nigeria says at least 50 terrorists killed

The Nigerian military said a day after the attack that it had killed at least 50 terrorists during clashes at the base, mentioning the death of two soldiers.

The military said the terrorists were killed as forces fought off a coordinated assault on the headquarters of its brigade in the town of Buni Gari, as well as a nearby checkpoint in Yobe state.

An intelligence source confirmed the attack and the army's counteroffensive to AFP.

Another intelligence source last week said casualties, both dead and wounded, had been taken to Maiduguri, the capital of neighbouring Borno state, in six ambulances.