Updated

LAGOS, Nigeria-- A bomb disposal officer was killed trying to defuse a bomb just minutes after another blast in a flashpoint central Nigeria city previously hit by a feared Islamist sect, police said Tuesday.

The first blast occurred Tuesday morning near a pedestrian bridge in a residential neighborhood in Kaduna and left no casualties, said Kaduna state police spokesman Aminu Lawan.

However, an officer from the police's anti-bomb squad was checking the contents of a plastic bag on the site, about 30 minutes after the first blast. A bomb inside the bag exploded, killing him instantly, Lawan said.

A radical Islamist sect known as Boko Haram claimed responsibility for another series of bomb attacks targeting two major military bases and a highway overpass that wounded an unknown number of people in Kaduna.

The blasts come amid an increase in sectarian attacks by Boko Haram. Its members have been blamed for killing at least 286 people this year alone, according to an Associated Press count.

The sect's violence comes as part of a campaign which its leader, Abubakar Shekau, says is aimed at avenging Muslim deaths and pushing for strict Shariah law across multiethnic Nigeria, a nation of more than 160 million people.

The northern-based Islamic insurgency has amplified insecurity in a state that sits on Nigeria's dividing line between its largely Christian south and Muslim north.

Kaduna was at the heart of postelection violence last April. Mobs armed with machetes and poison-tipped arrows took over streets in several parts of the state to protest the declaration that President Goodluck Jonathan, a Christian from the south, had won the polls. Followers of his main opponent, former military ruler Muhammadu Buhari, a Muslim from the north, quickly alleged the vote had been rigged, though observers largely declared the vote fair.

At least 800 people died across Nigeria in that rioting and at least 680 of them were killed in Kaduna, Human Rights Watch said. Heavily armed soldiers remain on guard on roadways across the central Nigerian state.

Before the elections, Kaduna had already proven to be one of the country's religious flashpoints. In 2002, rioting over a newspaper article suggesting the prophet Muhammad would have married a Miss World pageant contestant killed dozens here. In 2000, more than 2,000 died as the government moved to enact Islamic Shariah law.

Analysts say growing insecurity across Nigeria's north is fueled by poverty. About 69 percent of Nigeria's population in 2010, or about 112 million Nigerians, lived in poverty, Nigeria's National Bureau of Statistics said Monday, after studies showed that the oil-rich country's poor are getting poorer. In the study, northern Nigeria recorded the highest poverty rates.