The Nigerian military says it has repelled an attack against the country’s main army barracks in the country’s north, where anti-government fighters are held.

Hundreds of militants reportedly attacked the Giwa barracks in the northern city of Maiduguri on Friday.

“The attack has been successfully repelled with heavy human casualty on the terrorists,” said Nigerian Defense Ministry spokesman Brig. Gen. Christ Olukolade.

Nigerian army sources said the attack was an attempt to free anti-government prisoners.

The military has not confirmed whether any inmates had managed to get away.

Residents of the northern city say people on both sides were killed in the confrontation.

The Nigerian government has been engaged in a battle against members of the Boko Haram group for about five years.

The Boko Haram group has claimed responsibility for a number of deadly shooting attacks and bombings in various parts of Nigeria since 2009. The group aims to topple the Nigerian government, which it accuses of being pro-Western.

Over the past few years violence in the north of Africa’s most populous country has claimed the lives of more than 3,500 people, including killings by security forces.

The attack comes shortly after Human Rights Watch said in a report that attacks carried out by Boko Haram were having a “devastating impact on northern Nigerians.”