Reuters news service quoted university spokesman Mustapha Zahradeen saying that two university professors were killed in the Kano attack.

Sunday’s attack followed bombings Thursday at two offices of the daily newspaper This Day in the capital, Abuja, and in Kaduna, which killed at least seven people. Boko Haram claimed responsibility for those attacks.

There was no immediate claim of responsibility for the killings, but the assault was similar to previous attacks by Boko Haram, an Islamic extremist group. At least 450 people have died in attacks this year, according to Associated Press.

Gunmen in a car and on motorcycles threw homemade bombs at Christians gathered on the campus of Bayero University and shot them as they tried to flee, according to agency reports.

JOHANNESBURG, South Africa -- A terrorist attack at a university in the northern Nigeria city of Kano on Sunday left as many as 20 Christian worshipers dead and dozens of other people wounded.

This story has been updated. See the note below.

[Updated April 29, 3:44 p.m.: The Associated Press later reported that gunmen also opened fire at a Church of Christ in Nigeria chapel in the northeast city of Maiduguri, killing five people, including a pastor preparing for Communion. The report was based on statements by witnesses who requested anonymity for security's sake and could not be independently confirmed. No one immediately took responsibility.]

Boko Haram means “Western education is a sin,” with the militants bitterly opposed to teachings in secular education that, in its view, contradict Islam. The group, which bases itself on Afghanistan's Taliban and is believed to have links with an Al Qaeda affiliate in Mali, has escalated its activities since 2010, launching frequent terror attacks in the north of the country targeting the military, police, politicians and Christians.

The group recently warned Christians to leave the north, an area traditionally dominated by Muslims, for the predominantly Christian south. The extremists carried out terrorist attacks on churches at Christmas, killing 44 people, and at Easter, killing 41.

Nigerian forces have a heavy presence across the north and security has been stepped up at churches, yet authorities seem powerless to stop the attacks.

Attempts at peace talks with the militants, who hope to bring down the government and impose Islamic Sharia law across the country, have so far failed.

On Saturday, Nigerian President Goodluck Jonathan visited the Abuja office of This Day following the bombing.

Jonathan, who has vowed to crush Boko Haram by the end of June, told reporters the government would do everything necessary to stop the attacks. He would not confirm whether attempts to negotiate with the group were still going on.

“Just like a war situation, you may dialogue, you may not dialogue, depending on the circumstances. But we will exploit every means possible to bring this to an end,” the president told reporters.

Sunday saw another attack on churchgoers in Kenya when a man walked into a church and threw a grenade, killing one and wounding some 15 people, according to news agencies. It was not clear who was responsible for the attack.

There have been several grenade attacks in Kenya by Islamic extremists linked to the Somali terrorist group Al Shabab, but some reports suggested Sunday’s attack could be linked to a land dispute involving the church.

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-- Robyn Dixon

Photo: Nigerian President Goodluck Jonathan, center, and This Day owner Nduka Obaigbena, left, on Saturday visit the site in Abuja of a suicide attack on the newspaper's office last week. Credit: Wole Emmanuel / Agence France-Presse / Getty Images.