At least 12 people have been killed on Sunday as government forces repelled multiple attacks by Boko Haram in at least four different axis of the northern city of Maiduguri, capital of Nigeria's Borno State, local hospital sources told Xinhua.

Some 37 people have also sustained various degrees of injury from the attacks which started early Sunday.

Sources at the State Specialist Hospital in Maiduguri and another state-run health facility said the casualties included civilians who were hit by stray bullets.

A medical doctor in one of the hospitals said a man and two of his workers were brought in dead after the Boko Haram fighters fired a grenade which strayed into their apartment.

However, it could not be confirmed if the other casualties were government forces, Boko Haram fighters or the youth volunteer force, who joined in the gun fight to assist the military in pushing away the insurgents.

The Boko Haram fighters, armed with high-power weapons including two armored fighter vehicles, attacked the capital city through Njimtilo, a location on the outskirts of Maiduguri, from which it launched a similar attack exactly a week ago, according to Murtala Ahmed, a local resident.

Government troops responded quickly to the attacks, said a senior military officer, who pleaded for anonymity. The security source said the attack had spread to Mulle, Dalwa and Ngom areas of the northeastern state.

The attacks have caused panic in Borno State, particularly in the capital Maiduguri and the surrounding communities. Major roads have been cordoned off by security operatives and residents were advised to stay indoors as the attacks continue to spread.

A military personnel said the Boko Haram fighters were pushing hard to take control of the major city but met a stiff opposition in the government troops. The government forces had done more harm to the insurgents, the military personnel added.

Last week, a similar attack on Maiduguri by the Boko Haram group forced the Nigerian defense headquarters to impose a curfew on the city.

Maiduguri is the known headquarters of Boko Haram, which has proved to be a major security threat in Nigeria, Africa's most populous country.

The militant group has killed thousands of people in its five- year insurgency in Nigeria.