Bystanders in Zaria, Nigeria, look on at the scene of a bomb blast on Monday morning [Reuters]

At least 12 people are thought to have been killed and several others injured following a series of blasts that hit cities mainly in northern Nigeria.

Police on Monday were investigating the blasts, which came less than 24 hours after the inauguration of Goodluck Jonathan, the Nigerian president.

The most deadly incident was in the northern city of Bauchi, where three blasts tore through a beer garden in a military barracks on Sunday night.

An emergency source speaking on condition of anonymity said that at least 10 people were killed in the blast, while the AFP news agency quoted an army officer as saying that at least 20 people were killed.

"By my estimation ... the number of people killed could not be less than 20. Scores of others were injured in the blasts which occurred at five-second intervals," the unnamed officer was quoted as saying.

At least 2,000 people were thought to have been attending the "mammy market" when the blasts went off.

Such markets, which include beer gardens and eateries, are commonly found at Nigerian barracks and are open to civilians.

Separate blasts

Another blast at a beer parlour in Zuba, on the outskirts of Abuja, killed at least two people and wounded 11, according to Yushau Shuaib, the spokesman for the National Emergency Management Agency.

Two other blasts hit the northern town of Zaria, home to Namadi Sambo, Jonathan's vice-president, leaving several people injured, including two children.

"There have been two separate blasts in Zaria: one at a beer parlour on Sunday night where two people were injured, and another one Monday morning in the old part of the city in which two children were injured," Aminu Lawal, a Kaduna state police spokesperson, said.

"It is not clear who is behind the two blasts. But we have cordoned off the two areas and our forensic experts have taken samples from the scenes for analysis."

No one has yet claimed responsibility for the blasts.

Bauchi state was among the hardest-hit during rioting last month in the wake of an election that saw Jonathan, a southern Christian, claim victory over Muhammadu Buhari, a Muslim from the north.

Tensions in Nigeria are fuelled by poverty, unemployment and religious differences in a country where an unreliable power supply has closed factories and caused the loss of tens of thousands of jobs in the textile industry alone over the last few years, especially in the north.