Two bombs exploded at the mosque of one of Nigeria's top Islamic leaders Friday, a week after he issued a call to arms to fight Boko Haram.
At least 120 people were killed and 270 others wounded when two suicide bombers blew themselves up and gunmen opened fire in the latest chapter of violence in the African country where bombings, kidnappings and assassinations have become a routine.
The blasts happened at the Grand Mosque in Kano, the biggest city in the Muslim north of the country, just as Friday prayers had got under way at about 2:00 pm (1300 GMT). The mosque is attached to the palace of the Emir of Kano, Nigeria's second most senior Muslim cleric.
The explosions came after civilian vigilantes in the northeastern city of Maiduguri said they foiled a bomb attack against a mosque, five days after two female suicide bombers killed over 45 people in the city.
"Two bombs exploded, one after the other, in the premises of the Grand Mosque seconds after the prayers had started," worshipper Aminu Abdullahi told AFP.
"A third one went off in a nearby road close to the Qadiriyya Sufi order. The blasts were followed by gunshots by the police to scare off potential attacks."
His account was backed up by another witness, Hajara Tukur, who said she lives nearby.
The emir, known officially as Muhammad Sanusi II, last week said at the same mosque that northerners should take up arms against Boko Haram, which has been fighting for a hardline Islamic state since 2009.
He also cast doubt on Nigerian troops' ability to protect civilians and end the insurgency, in rare public comments by a cleric on political and military affairs.
The Emir of Kano is a hugely influential figure in Nigeria, which is home to more than 80 million Muslims, most of whom live in the north.
Officially the emir is the country's number two cleric, behind the Sultan of Sokoto, and any attack could inflame tensions in Nigeria's second city, which is an ancient seat of Islamic study.
Sanusi was named emir earlier this year and is a prominent figure in his own right, having previously served as the governor of the Central Bank of Nigeria.
During his time in charge of the CBN, he spoke out against massive government fraud and was suspended from his post in February just as his term of office was drawing to a close.
Boko Haram has repeatedly attacked Kano. On November 14, a suicide bomb attack at a petrol station killed six people, including three police.
The Islamists have a record of attacking prominent clerics. In July 2012 a suicide bomber killed five people leaving Friday prayers at the home of the Shehu of Borno in Maiduguri.
The Shehu is Nigeria's number three Islamic leader.
Boko Haram threatened Sanusi's predecessor and the Sultan of Sokoto for allegedly betraying the faith by submitting to the authority of the secular government in Abuja.
In early 2013, the convoy of Sanusi's predecessor was also attacked.
Andrew Noakes, co-ordinator of the Nigeria Security Network of security analysts, said the attack fit a pattern of violence targeting religious and traditional leaders seen as "allies" of the state.
He said it was possible that the group carried out the attack as a direct response to Sanusi's comments last week, although it may have been planned beforehand.
"Whatever the case, the group has sent a message to northern leaders that crossing them will have consequences," Noakes said in an email exchange.
Boko Haram attacks in recent months have ranged from the far northeast of Nigeria, across the wider north and northwest, using hit-and-run tactics, suicide bombings and car bombs.
The authorities in Cameroon, Chad and Niger have all expressed concern about Boko Haram's ability to conduct cross-border strikes, particularly as the dry season approaches.
In Maiduguri, the capital of Borno state, civilian vigilantes said they had discovered a suspected remote-controlled device planted in the Gamboru Market area of the city.
It was successfully defused by the police bomb squad but as the bomb was being made safe, another device exploded nearby. There were no casualties, as the area had been cordoned off.
"Our assumption is that the bombs were planted ahead of Friday prayers in the mosque just nearby," civilian vigilante Babakura Adam said.
"Of course, it's Boko Haram's handiwork because in the last few days several arrests have been made of suspected female suicide bombers."
Adam said the arrests were made on Wednesday and Thursday.
Fears have grown in Maiduguri about an upsurge in Boko Haram attacks, after the militant Islamists took over more than two dozen towns in Borno and two neighbouring states in recent months.
The use of concealed roadside bombs would be a departure for Boko Haram, which has previously used direct hit-and-run tactics, car bombs and suicide attacks as part of its deadly campaign.