This was the third explosion in Gombe in two days
A car bomb has exploded outside a stadium in the Nigerian city of Gombe, minutes after President Goodluck Jonathan left a campaign rally there.
At least three people were killed and 18 others were wounded when the bomb exploded, hospital sources said.
Mr Jonathan is standing for re-election on 14 February against against former general Muhammadu Buhari.
The militant Islamist group Boko Haram has stepped up its attacks in the run-up to the contest.
Mohammed Bolari, who was at the rally in Gombe, said the explosion occurred some three minutes after Mr Jonathan's departure, AFP news agency reports.
"The president had just passed the parking lot and we were trailing behind his convoy when the explosion happened," he was quoted as saying.
Mr Jonathan addressed a rally in the north-eastern city a day after it was hit by two blasts that killed at least five people, AFP reports.
Since Monday morning, the city has largely been in lockdown with security operatives restricting the movement of people in most areas, Nigeria's privately owned Daily Trust newspaper reports.
A local journalist told AFP the latest blast had led to unrest in Gombe, with angry youths attacking supporters of Mr Jonathan's People's Democratic Party (PDP).
"They were shouting and denouncing the president's visit which they blamed for the attack," he added.
Northern Nigeria is seen as Mr Buhari's stronghold.
BBC