An explosion went off outside a nightclub in the Nigerian capital Abuja, breaking windows and damaging cars, but no casualties were reported, the country's emergency agency said on Saturday.

"No human casualty," Yushau Shuaib, spokesman for the National Emergency Management Agency, said of the blast late Friday. "The explosives were suspected to have been planted on a tree opposite Kryxtal Lounge."

An Islamist insurgency that has increasingly targeted churches has sparked fears of wider unrest in Nigeria after anger boiled over at the weekend, resulting in deadly riots by Christian mobs.

Christian leaders and others in Africa's most populous nation have warned in recent days that the government's failure to stop Islamist group Boko Haram could lead to more cases of residents taking the law into their own hands.

A suicide attack at the Abuja bureau of a top Nigerian newspaper and an attempted car bombing at another of its offices killed eight people Thursday in the first such strikes on the country's media.

The second attack hit the northern city of Kaduna. Later in the day, a third, smaller bombing also occurred in the same city, leaving three people wounded.

The U.S. embassy in Nigeria warned on Wednesday that Islamist group Boko Haram may be planning attacks in the capital Abuja, including against hotels frequented by Westerners.

"The U.S. embassy has received information that Boko Haram may be planning attacks in Abuja, Nigeria, including against hotels frequently visited by Westerners," an emergency message to U.S. citizens on its website said.

Bomb attacks on churches during Christmas services and a suicide blast killed at least 35 people in Nigeria on Sunday amid spiraling violence claimed by Islamists.

A purported spokesman for Islamist group Boko Haram claimed responsibility for a bombing of the church outside the Nigerian capital and other violence in recent days that has stoked fear and anger in Africa's most populous nation.

Nigeria marked the Muslim feast of Eid el-Adha amid fears and tears as the U.S. warned of possible new attacks after deadly blasts claimed by Islamists killed 150 people in the northeast of the country.

The attacks on Friday in Damaturu were among the deadliest ever carried out by Boko Haram, an Islamist sect based in the north of Africa's most populous country.

A suicide bomb blast rocked the U.N. compound in the Nigerian capital Abuja on Friday, killing at least 18 people, leaving others trapped and blowing out large areas of the building, officials said.

Witnesses reported that the bomb went off after a suspect rammed a car through the front gate. Parts of the first two floors of the building were blown out and rescue workers scrambled to rescue those left inside.