At least six people have been killed after two suspected child suicide bombers blew themselves up in a market in northeast Nigeria, witnesses say.

Sunday's assault was the second attack involving young girls strapped with explosives.

The blasts struck around mid-afternoon at an open market selling mobile handsets in the town of Potiskum in Yobe state, one of three northeastern states, after Adamawa and Borno, that have been hit by the armed group Boko Haram.

A trader at the market said the bombers were about 10 years old.

"I saw their dead bodies. They are two young girls of about 10 years of age ... you only see the plaited hair and part of the upper torso," he said.

The town was hit by a suicide bomber in November when at least 48 people, mainly students, were killed during a school assembly.

On Saturday, a bomb exploded at a police station in Potiskum.

Sunday's explosions came a day after a bomb strapped to a girl, aged about 10 years, exploded in a busy market place in the Nigerian city of Maiduguri, killing at least 16 people and injuring more than 20, security sources said.

Boko Haram, which opposes western influence and education, has been fighting since 2009 to establish an Islamic state in the northeast of the country.

The the army's inability to crush the movement has created problems for President Goodluck Jonathan, who is seeking re-election in February.

Last year more than 10,000 people died in the violence, according to an estimate by the New York-based Council on Foreign Relations.

The military lost ground in worst-hit Borno state last weekend after fighters took over the town of Baga and a nearby army base, killing over 100 people and forcing thousands to flee.

The defence headquarters said on Saturday that the army was regrouping to retake the area.

In the city of Jos in Plateau state, Jonathan's campaign team was hit by two days of violence.

The driver of a campaign vehicle was killed on Sunday by youths who also set fire to a police station, Abu Sunday Emmanuel, a police spokesman, said.

On Saturday, two other campaign vehicles were burnt.

Source: Agencies