More than 100 people died in an attack on a Nigerian mosque on Friday, local government and hospital officials say.

The president of Nigeria has vowed "to leave no stone unturned" in tracking down the perpetrators of the gun and bomb attack during Friday's prayers in the northern city of Kano.

Goodluck Jonathan urged the nation "to confront the common enemy".

No-one has so far claimed the attack but officials say it bears the hallmarks of Boko Haram militant group.

Kano's Central Mosque, where the attack took place, is where the influential Muslim leader, the emir of Kano, usually leads prayers.

Emir Muhammed Sanusi had recently called for people to arm themselves against Boko Haram, and there have been suggestions that the attack was in response to that call.

However, on Saturday the emir dismissed the claims, saying it must have taken at least two months to plan the attack. He made the comments during a visit to the mosque.

Boko Haram, a Sunni Islamist group, has been waging an insurgency in Nigeria since 2009 and has killed more than 2,000 people this year, human rights groups say.

'Common enemy'

President Jonathan ordered the country's security services "to launch a full-scale investigation and to leave no stone unturned until all agents of terror undermining the right of every citizen to life and dignity are tracked down and brought to justice".

 A number of the injured are being treated at Kano's hospital

 Eyewitnesses spoke of three bomb explosions and a gunfight near the mosque

He said Nigerians should "remain united to confront the common enemy".

The government, he said, would "continue to take every step to put an end to the reprehensible acts of all groups and persons involved in acts of terrorism".

Three bomb explosions were reported in and around the mosque. The attackers also shot at worshippers.

Some reports say the first bomb was hidden in a car which was driven straight into the worshippers.

One eyewitness told the BBC's Focus on Africa: "The imam was about to start prayer when he saw somebody in a car trying to force himself into the mosque. But when people stopped him, he detonated the explosions. People started running helter-skelter."

Several men then opened fire on the crowd, killing more people. Three of the gunmen were then killed by the crowd, our correspondent says.

Most victims were men or boys with blast injuries and severe burns.

Boko Haram has stepped up attacks against civilian targets since the Nigerian military launched an offensive last year.

The group carries out almost daily attacks mostly in the north-east of the country.

The militants were also behind the kidnapping of more than 200 schoolgirls from Chibok in Borno state this year, an act that sparked international outrage.

 Boko Haram leader Abubakar Shekau has declared an Islamic state in the north-east