People search for survivors at the scene of a bomb explosion in Nigeria's Kaduna city (Reuters)

A bomb disposal officer was killed by a blast as he tried to defuse an explosive in the Nigerian city of Kaduna, shortly after another explosion in the area.

Nobody was hurt in the first blast by a bridge in a residential area of the city, a Kaduna police spokesman told Associated Press.

Boko Haram, a radical Islamist sect, claimed responsibility for the bombings.

The officer killed was part of the anti-bomb squad.

He was checking a suspicious plastic bag around half an hour after the first explosion.

Suddenly the bag's contents blew up, killing him instantly.

This is just the latest in a string of attacks by Boko Haram, which have claimed the lives of 286 people in 2012 alone.

The group's leader, Abubakar Shekau, claims the violence is in response to Nigerian Muslims' deaths and to put pressure on the country's leadership to introduce a strict version of Shariah law.

Around 680 people died in Kaduna in April 2011 following riots over the election of Christian Goodluck Johnson as Nigeria's president.

Christians from the south and Muslims from the north clashed in the central Kaduna state.

Heavily armed soldiers are still on guard on roadways across the area.