Sporadic shootings were heard on Sunday as government forces repelled an attack by suspected Boko Haram fighters who attempted to capture the northern city of Maiduguri, capital of Borno State in Nigeria's northeast region, local residents and security sources said.

Armed with high-power weapons, the Boko Haram members invaded the capital city but met a stiff opposition in the government forces, Musa Abubakar, a resident told Xinhua by telephone.

A military fighter jet hovering the area has continued to wreak havoc in the camp of the insurgents, said the resident, noting the gun blasts were still ongoing. The country's Defense Headquarters said it has imposed a curfew on Maiduguri with immediate effect. The insurgents invaded the state capital through Njimgilo, an entrance of Maiduguri, also known as the headquarters of Boko Haram, a terror group which has proved to be a major security threat in Nigeria.

A Nigerian air force personnel, who pleaded for anonymity, said the government forces had done more harm to the insurgents. However, no casualties figure has so far been given on the gun fight.

Sources said the incident had caused panic among residents of the state capital. A resident named Timothy Olanrewaju said he was turned back home on his way to church by fierce-looking security men who blocked the major roads in the city.

Sunday's attack occurred barely 24 hours after Nigerian president Goodluck Jonathan visited Maiduguri to canvass for votes in his bid for re-election in next month's presidential election in the West African country. The president has said he would get rid of insurgents in the northeast region of the most populous country in Africa.

Boko Haram had recently taken over some cities in the northeastern region of Nigeria. Early this month, Baga Town, also in Borno State, was under the control of the insurgents for more than one week.

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