US Secretary of State Hillary Clinton said Tuesday the United States "strongly condemns" a deadly attack on worshipers at church services in Nigeria as well as other attacks on civilians.

On Sunday, attackers with bombs and guns opened fire at church services at a Nigerian university in the northern city of Kano, killing around 20 people as worshippers tried to flee, witnesses and officials said.

"The United States strongly condemns the recent attacks on innocent civilians in Nigeria, including yesterday's disgraceful assault during church services at Bayero University in Kano," Clinton said in a statement.

"We are concerned about attacks on churches, news media, and government installations that increasingly target innocent civilians across northern Nigeria," said Clinton, who is currently en route to China.

"We condemn attempts by those in Nigeria who seek to inflame Christian-Muslim tensions, and support those who recognize Nigeria's ethnic and religious diversity as one of the country's greatest strengths," she said.

Nigeria, Africa's most populous nation and largest oil producer, is roughly divided between a mainly Muslim north and predominantly Christian south.

Suspected in Sunday's attacks is Boko Haram, which initially claimed to be fighting for the creation of an Islamic state in Nigeria's north, but its demands and structure have become less clear in recent months.

Nigerian troops killed a suspected Boko Haram militant Tuesday during a pre-dawn raid in the city of Kano over the weekend attacks against church services.

AFP