Suspected members of the Boko Haram Islamist sect killed the attorney general of Nigeria's northeast state Borno overnight, the state's justice ministry said on Tuesday, a day after the sect's spokesman was reportedly killed in a shootout.

Boko Haram, which models itself on the Afghan Taliban, is fighting to create an Islamic state in largely Muslim northern Nigeria, a battle in which the sect has killed hundreds of people in gun and bomb attacks. Its headquarters is in Borno.

Zanna Malam Gana was shot dead in his home town of Bama, in Nigeria's remote northeast, on the threshold of the Sahara Desert, the justice ministry said in a statement to local journalists. It said his burial would take place on Tuesday.

On Monday, a Nigerian security source said its forces had killed Abu Qaqa, the main spokesman of the Boko Haram sect, which has become the biggest threat to Nigeria's security, as well as another senior militant.

There has been no response from the sect on the claim. Nigerian forces have claimed to have killed or captured him before, only for the militant to issue a statement denying it.

Boko Haram traditionally targets authority figures or security sources, although it started attacking mobile phone installations across the northeast two weeks ago, saying phone companies were helping authorities to track down its fighters.

They have already destroyed around 30 phone masts.

MTN Nigeria said in a statement on Tuesday that due to sabotage it had also "experienced multiple cuts to its fibre cable in the same region, which has impacted service in the eastern part of the country".

"Current security concerns have prevented not only repair work to damaged equipment, but routine maintenance, causing disruption to the lives of millions of Nigerians," MTN Nigeria's general manager of corporate affairs, Funmi Omogbenigun, said.

A military crackdown in the north appears to have damaged Boko Haram's capabilities, although it remains deadly in many parts. At least 186 people died in coordinated attacks in the north's main city of Kano in January.