Authorities have declared a 24-hour curfew in the Nigerian city of Kaduna after two blasts targeting opposition and Muslim leaders killed at least 42 people.

The first explosion on Wednesday targeted a convoy of a prominent Muslim cleric Dahuru Bauchi, killing 25 people. A second blast hours later targeted opposition leader Muhammadu Buhari in a market area, killing at least 17 people.

The Reuters news agency reported a death toll of 50 for the second blast, as witnesses also claimed a much higher figure than that provided by police.

Buhari, the leader of the All Progressives Congress party, and Bauchi, a cleric who has publicly criticised the Nigerian armed group Boko Haram, were unhurt in the attacks.

Ahmed Maiyaki, a spokesman for the state government, said a 24-hour had been imposed on Kaduna.

"The measure is aimed at forestalling breakdown of law and order", he said, adding the attacks had been carried out "by the agents of darkness".

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In a statement, Buhari called it "clearly an assassination attempt" when an attempt was made to ram into his car in a market area, whereby a bomb went off that "destroyed all three cars in our convoy".

"Unfortunately, when I came out of my vehicle I saw many dead bodies ... innocent people going about their daily business," said Buhari.

In a statement, President Goodluck Jonathan denounced "the dastardly targeting of the prominent political and religious leaders by terrorists and enemies of the nation".

He also said the government would continue and intensify its efforts "to curb the menace of terrorism."

There was no immediate claim of responsibility, but Boko Haram has been staging attacks, especially with explosives, outside its northeastern heartlands in the past three months.

Jonathan, facing unprecedented pressure to contain the bloodshed, has asked parliament to approve a $1bn foreign loan to upgrade the security services.

Some analysts have described the request as a tacit acknowledgement by the president that his military is overmatched by Boko Haram who are blamed for killing more than 10,000 people since 2009, according to AFP.

Source: Al Jazeera and agencies