Two bomb blasts in the north Nigerian city of Kaduna killed at least 82 people, officials said, in attacks that bore the hallmarks of violent Islamist group Boko Haram.

A bomb blast killed 50 people in the crowded Kawo market, a local Red Cross worker on the scene, who declined to be named, said.

Nigerian opposition leader Muhammadu Buhari, who also led the country as a military dictator in the 1980s, was the target of the attack, an official said.

Ahmed Maiyaki, spokesman for Kaduna's governor, told AFP that Mr Buhari "was the target" of the bombing in the Kawo area of the city. 

Mr Buhari, who came runner-up to President Goodluck Jonathan in Nigeria's 2011 elections, is a leader of the All Progressives Congress and may emerge as the party's presidential candidate in polls set for next year. 

An earlier suicide bomber targeting a moderate Muslim cleric killed at least 32 of the cleric's congregation on a busy commercial road.

Thousands were gathered for prayers with Sheikh Dahiru Bauchi in Murtala Muhammed square, and when his convoy pulled up, the bomber lunged at him before being stopped by his private security, witnesses and police said.

"The attack was targeted at the sheikh. No arrest has been made yet," said police commissioner Shehu Umar.

The bomb did not injure Mr Bauchi, several witnesses told Reuters. Mustafa Sani, a volunteer for Mr Bauchi's mosque, who was evacuating bodies said there were 32 confirmed dead so far.

"Somebody with a bomb vest ... was blocked. He detonated the bomb along with the person that tried to block him," Mr Umar said, adding that police had only been able to confirm 25 dead, with 14 wounded.

Police sometimes give lower casualty tolls than workers on the scene.

A Reuters reporter saw blood and body parts scattered on the Alkali Road in the city centre.

The military used pick-up trucks to cordon off the area. Sirens wailed as fire engines raced to the scene.

An angry crowd started throwing stones at police, who responded by dispersing them with tear gas. Some followers had come from Senegal, Chad and Niger to see the popular sheikh.