AFP/Kano

Nigerian President Goodluck Jonathan vowed on Saturday to hunt down those behind "heinous" attacks that killed at least 120 at the mosque of an Islamic leader who issued a call to arms against Boko Haram.

At least 270 others were also wounded when two suicide bombers blew themselves up and gunmen opened fire during weekly prayers on Friday at the Grand Mosque in Kano, the biggest city in the mainly Muslim north of the country, according to a toll given to AFP late Friday by a senior rescue official.

Jonathan  "directed the security agencies to launch a full-scale investigation and to leave no stone unturned until all agents of terror... are tracked down and brought to justice," said a statement from his office on Saturday.

The mosque is attached to the palace of Kano's emir, Muhammad Sanusi II, Nigeria's second most senior Muslim cleric, who last week made a call at the same mosque urging civilians to take up arms against Islamist extremists Boko Haram.

Sanusi on Saturday returned from abroad to inspect the mosque.

"From all indications, they (the attackers) have been planning this for at least two months," Sanusi told reporters at the airport without elaborating.

"I have directed that the mosque be washed and cleaned and prayers should continue here," the emir said.

"We will never be intimidated into abandoning our religion, which is the intention of the attackers."

The attack, though, was widely seen inside Nigeria as revenge for the emir's call against Boko Haram.

"It was death and blood all over. People lay dead and others shrieked in horror and pain," one survivor, Muhammad Inuwa Balarabe, told AFP from his hospital bed on Saturday.

"I was inside the premises of the mosque. As soon as the prayer started, a bomb went off. They just started shooting people," said the 32-year-old tailor, who received serious burns to his thighs.

Jonathan urged Nigerians "not to despair in this moment of great trial in our nation's history but to remain united to confront the common enemy".

- Intensifying attacks -

"One wonders what kind of religion these people practise," said survivor Maikudi Musa, who lost a sibling in the blast and saw another badly hurt.

"You can't justify attacking and killing defenceless people at will in the name of religion."

Just hours before the Kano massacre, a suspected remote-controlled roadside bomb near another mosque nearly 600 kilometres (380 miles) away in Maiduguri, was defused.

Maiduguri, where Boko Haram was founded in 2002, was already tense after two female suicide bombers wreaked havoc at a crowded market on Tuesday, killing more than 45 shoppers and traders.

More than 13,000 people are thought to have died in total since the insurgency broke out in 2009.

- 'Out of control Boko Haram' -

After the latest attacks, the special representative of the UN Secretary-General for west Africa, Mohamed Ibn Chambas, called on Nigerian authorities "to increase their response against terrorist threats in northeastern Nigeria", and for additional measures to protect civilians.

UN chief Ban Ki-moon condemned the bloodshed at the mosque, saying in a statement that "there can be no justification for attacks on civilians".

The French foreign ministry decried the "barbaric" attack, while the US State Department called it "horrendous" and said the United States "stands with the Nigerian people in their struggle against violent extremism".

A Nigerian security expert, Ona Ekhomu, told a TV debate that the latest attacks showed that "we are at war in Nigeria".

In the same programme, national police spokesman Emmanuel Ojukwu said: "We try to prevent crimes from happening... but criminals sometimes beat the security."

With northern Nigeria gripped by fear, neighbouring Cameroon, Niger and Chad are also concerned that the violence could spread across their borders.