A bomb exploded outside a church in Maiduguri in northeast Nigeria on Sunday, reviving concerns about a radical Islamist sect in the remote region of Africa's most populous nation.
No one was confirmed dead but hospital staff said they had treated some wounded, including one soldier.
"The bomb was planted near a church where our boys were on guard but fortunately no casualties were recorded," the operations officer for a joint military task force said.
He did not confirm whether the blast was carried out by Boko Haram, a sect whose name means "Western education is forbidden" and which has been behind almost daily shootings or attacks with homemade explosives in recent months.
The sect's ambition has grown and Nigerian and foreign officials have said the group has strengthening links with al Qaeda's North African wing.
Boko Haram took responsibility for Nigeria's first successful suicide attack in August, when the driver rammed a car full of explosives into the side of UN headquarters in the capital Abuja, killing 23 people.
Since the UN blast security has been increased in all major towns and cities and scores of suspected members of Boko Haram have been arrested, some facing trial this month for their part in deadly bombings.
The crackdown reduced the number of attacks in the sect's home base in the dusty northeast but at least two people were killed in a gunfight last week and Sunday's blast was a reminder of the threat still posed by bombers.
"We thought peace has come to stay and there won't be any more bombs. I am getting my family out of this place tomorrow, I've had enough of Maiduguri," said Okechukwu, a pharmacy owner said.