Two blasts rocked a northern Nigerian city Tuesday, including one targeting a military barracks, but the number of casualties was not immediately clear, officials said.

The explosions occurred in Kaduna, a major city in Nigeria's mainly Muslim north, a region hit by scores of attacks blamed on Islamist group Boko Haram. The cause of the blasts was not clear.

"There were two separate blasts," said Musa Ilallah, an official with the National Emergency Management Agency in Kaduna, with one near a bridge and the other "inside the 1st Mechanised Division of the Nigerian army."

He said rescue officials had been deployed but were being refused access to the area by soldiers.

"From all indications, they gate-crashed into the military barracks," said Ilallah, adding that there was talk of a suicide bomber, but that there was no official confirmation.

Residents said windows at an office complex at the military barracks were shattered. The area had been cordoned off, but the office complex could be seen, residents said.

"Virtually all the glass has been shattered," one resident said. "I saw soldiers with glass cuts on their bodies being taken out, but it's difficult to say if there were any (more serious) casualties."

Boko Haram has been blamed for scores of bomb attacks in northern Nigeria, including some in Kaduna, a major city in Nigeria's mainly Muslim north.

It claimed responsibility for January 20 coordinated bombings and shootings in Nigeria's second-largest city of Kano that left at least 185 people dead -- Boko Haram's deadliest attack yet.

The August suicide bombing of UN headquarters in the capital Abuja which killed at least 25 people was also attributed to the group.

In December, a powerful explosion rocked Kaduna, killing at least eight people, wounding many others and destroying a number of houses and shops, but the cause has never been clarified.

Police initially said the December explosion appeared accidental, but speculation over whether it was caused by a bomb intensified due to the blast's strength and rumours spread through the city over who may have been the target.

Kaduna has been on edge since being hit by some of the worst rioting following April elections won by President Goodluck Jonathan, a Christian from the south.

Three days of deadly rioting across the north killed some 800 people.

Nigeria, Africa's most populous nation and largest oil producer, is roughly divided between a mainly Muslim north and predominantly Christian south.

Boko Haram has claimed to be fighting for an Islamic state in Nigeria's north, but its demands have varied.