The United States and Britain on Sunday warned of a possible terrorist attack in Nigeria's federal capital Abuja, especially aimed at government buildings, places of worship and schools, among other targets.

Nigeria is fighting an Islamist insurgency mainly in the northeast, but in July the Islamic State claimed responsibility for a raid on a prison in Abuja, which freed around 440 inmates, raising fears that insurgents were venturing from their enclaves.

The U.S. Embassy in Nigeria said "there is an elevated risk of terror attacks in Nigeria, specifically Abuja" and added that shopping malls, law enforcement facilities and international organisations were among places at risk.

"The U.S. Embassy will offer reduced services until further notice," the embassy said in an alert to citizens in Nigeria.

The United Kingdom government warned that its citizens in Nigeria should stay alert due to an "increased threat of terrorist attack in Abuja."

"Attacks could be indiscriminate and could affect western interests, as well as places visited by tourists," it said.

Insecurity, which has spread across Nigeria, is a major issue for voters when they go to the polls next February to elect a new president to succeed President Muhammadu Buhari.

Nigeria's foreign affairs ministry was not immediately available to comment.

Reuters