Abuja: A leader of Nigeria's fundamentalist Islamic sect Boko Haram has vowed to carry out more attacks on the country in a video message, challenging the authority of President Goodluck Jonathan.

Sitting between two Kalashnikiv rifles, Imam Abubakar Shekau chided the oil-rich African country's President Jonathan for criticising the activities of the group, arguing that his sect was popular in northern Nigeria.

Shekau, who wore military camouflage, said the killings carried out by his sect were done with the help of Allah.

"All these things you've been seeing happening, it's Allah who has been doing it because you refuse to believe in him and you misuse his religion and because of that, the thing is more than you, Jonathan," he said in Hausa language spoken widely in northern region of the country and neighbouring Niger and Chad.

"People are talking about us, that we are a disease, a cancer, to people in Nigeria," Shekau says.

"But we are not cancer and we are not a disease. And we are not wicked people with a bad habit. If people do not know us, Allah knows us," he added even as he criticised Christian leaders for calling on their members to prepare to defend them.

The group warned southern Christians to leave the north with a bomb attack at a Church in Abuja killing tens of worshippers.

Militants of the group also attacked a bus conveying southerners fleeing the north and killed four persons.

The activities of Boko Haram have raised fears of religious conflict in the country since the Christmas day bombing that killed not less than 40 persons in a church and several parts of the north.

Boko Haram has been waging a bloody conflict to install an Islamic government and Sharia rule in the country.

A suicide bomb attack by the group at the United Nations headquarters in Abuja in July killed 26 persons.

While Muslims are predominant in the northern part of Nigeria, Christians are dominant in the South.