Suicide bombers strike bus stations in the north of the country leaving at least 22 dead and scores wounded.

Suicide bombers have struck two bus stations in different parts of northern Nigeria, killing at least 22 people and wounding scores.

In the first explosion, a suicide bomber rushed onto a bus in the town of Potiskum before setting off a blast that killed at least 12 people and injured 35 others.

"The bus had just loaded with passengers on its way to Kano when a huge explosion happened inside the bus at exactly 11:40 am," a driver's union official told the AFP news agency.

Waziri Danu, who lives in the area, told AFP he was at a car wash nearby when he heard a huge explosion and saw fire and smoke coming from the motor park.

"I and people around rushed to the place and we saw a bus engulfed in flames.... It is not likely if anyone in the vehicle has survived."

In the second attack, two suicide bombers launched a coordinated strike on a major bus station in the city of Kano, killing at least 10 people, police spokesman Ibrahim Idris said.

No one has claimed responsibility for either bombing.

Potiskum, the commercial capital of Yobe state, has been hit repeatedly by bombings

On Sunday, a young girl, believed to have been aged seven, blew herself up at a crowded market in the city.

Boko Haram fighters have increasingly used young girls and women as human bombs, with so-called "soft targets" such as markets and bus stations.

The latest blasts underline the severe security challenges facing Nigeria in the run-up to presidential and parliamentary elections on March 28.

The elections were initially scheduled for February 14 but were delayed by six weeks to give the military and its allies more time to secure and stabilise the northeast to allow people to vote.

Missionary kidnapped

Meanwhile, the Methodist Church and security sources said on Tuesday that a US woman working as a Christian missionary had been kidnapped overnight.

"Early this morning we received a report that Reverend Phyllis Sortor, our missionary in Nigeria, was abducted from the Hope Academy compound in Emiworo, Kogi State, Nigeria by several persons," the church said on its website.

A US State Department official said authorities had heard the reports but could not make further comments in the interest of privacy.