KANO, Nigeria: Gunmen opened fire and threw explosives at a police station in the Nigerian embattled city of Kano on Tuesday, residents said, four days after coordinated bombings and shootouts killed 185 people there.
"It was around 6:30 (pm) when people were preparing for the evening prayers and a large group of gunmen arrived in the area and opened fire on the police station and threw in bombs," said a resident of the Sheka area of the city.
It was unclear if there were casualties.
Another resident said he could see fire coming from the building in the city still reeling from Friday's attacks that targetted mainly police buildings.
Friday's wave of attacks in Kano were the deadliest operation launched by Islamist sect Boko Haram since it began a bloody campaign in July 2009 which Human Rights Watch said Tuesday has left close to 1,000 people dead.
The US State Department urged Africa's most populous nation and top oil producer to "stand united" in the face of growing sectarian strife, while a visiting US delegation promised security assistance.
Earlier gunfire erupted when security forces raided a house suspected to be a Boko Haram hideout shortly after midnight.
They opened fire and a suspect fired back resulting in a shootout lasting around four-and-half hours.
"Everybody in the neighbourhood was in fear. We couldn't sleep," said a resident.
Nine attackers, at least five of them suicide bombers, died in the Friday onslaught.
Human Rights Watch said "Boko Haram's attacks show a complete and utter disregard for human life" and urged the authorities to put an end to the violent campaign.
According to the New York-based rights group, Boko Haram has killed more than 935 people since the group -- whose name can be loosely translated as "Western education is sin" -- launched a violent campaign in July 2009.
More than 250 of those deaths have come in 2012 alone.
"This is a time for all Nigerians to stand united against the enemies of civility and peace," US State Department spokeswoman Victoria Nuland said in a statement.
She also urged the Nigerian authorities to fully investigate the attacks, including those against Christians, and hold the perpetrators accountable.
A US delegation led by William Fitzgerald, the deputy assistant secretary of state for African affairs, and Joseph McMillan, the principal deputy assistant secretary for defence, held security talks with Nigeria in the capital Abuja on Tuesday.
The two sides agreed to boost the operational capabilities of the Nigeria security services in the face of internal security threats. They would consider training, intelligence sharing and modernisation of the security services.
Boko Haram which has staged a series of increasingly sophisticated and bloody attacks, often targeting security agencies and lately Christians, is believed to have a number of factions with differing aims, including some with political links and a hardcore Islamist cell.
A top African Union official warned of the possibility of the radical sect spreading its violence campaigns to other African countries.
"The possibility of this group expanding its activities into the neighbouring countries, deep into the Central African region should not be discarded," said Francisco Caetano Jose Madeira said, who is in charge of counter-terrorism cooperation for the AU, said in Abuja.
Officials from Sahel states in a meeting also attended by Nigeria in the Mauritanian capital Nouakchott vowed to help each other fight Al-Qaeda in the Islamic Maghreb and Boko Haram, amid growing speculation the two have ties.
Mali's Foreign Minister Soumeylou Boubeye Maiga said there was a "confirmed link" between AQIM and Boko Haram.
Amnesty International urged Nigeria to do more to protect its citizens from Boko Haram attacks.
President Goodluck Jonathan vowed to beef up security as he grapples with the worst crises of his nine-month tenure -- a surge in Boko Haram attacks and mounting social discontent.
A purported spokesman for Boko Haram said the attacks were in response to a refusal by the authorities to release arrested members of the group from custody.