LAGOS, Nigeria -- Two explosions struck Tuesday near army and air force bases on the outskirts of the central Nigerian city at the heart of riots last year that killed hundreds, officials said.

The explosion near the city of Kaduna caused an unknown number of injuries, said Yushau Shuaib, a spokesman for Nigeria's National Emergency Management Agency. Shuaib said officials were trying to cordon off the area.

Emergency officials confirmed the blasts occurred at the base of the 1st Mechanized Division near the town of Kawo and at the air force's training base near Mando. The officials declined to be named given the sensitivity of the matter.

Army and air force spokesmen could not be immediately reached for comment.

The blasts come as Nigeria faces increasingly bloody attacks from a radical Islamist sect known as Boko Haram.

Kaduna, on Nigeria's dividing line between its largely Christian south and Muslim north, was at the heart of postelection violence in April. Mobs armed with machetes and poison-tipped arrows took over streets of Kaduna and the state's rural countryside after election officials declared President Goodluck Jonathan the winner. Followers of his main opponent, former military ruler Muhammadu Buhari, a Muslim, quickly alleged the vote had been rigged, though observers largely declared the vote fair.

Across the nation, at least 800 people died in the April rioting, Human Rights Watch said.

In Kaduna alone, more than 2,000 died as the government moved to enact Islamic Shariah law in 2000. In 2002, rioting over a newspaper article suggesting the prophet Muhammad would have married a Miss World pageant contestant killed dozens.