Three bomb blasts hit the northern Nigerian cities of Maiduguri and Damaturu on Wednesday just days after the areas were placed under a state of emergency, the military and witnesses said.
No casualties were immediately reported after the attacks, claimed by the Islamist sect Boko Haram, as its ultimatum expired for Christians living in the mainly Muslim north to move south.
Two civilians were shot dead in a separate incident, a hospital source said.
The attacks were the first incidents in the area since President Goodluck Jonathan declared a state of emergency last weekend in parts of the country hard hit by Boko Haram.
Abul Qaqa, who claims to be a spokesman for Boko Haram, said the group was behind the Damaturu and Maiduguri bomb attacks. His claims could not be independently verified.
"We are responsible for the bomb blasts in Damaturu and Maiduguri this evening," he said in a phone call made to AFP.
"This is a response to the expiration of the ultimatum we gave to southerners to leave."
On Sunday, the purported spokesman for Boko Haram warned that the group would confront soldiers and threatened Christians living in the country's north.
He gave southerners living in the north three days to leave the region in the wake of Jonathan's state of emergency decree.
Lieutenant Colonel Hassan Mohammed, spokesman for a special military taskforce in Maiduguri, told AFP Wednesday: "There were two explosions in the Mairi area... this evening. The explosives were planted in a ditch and detonated when nobody was around."
The blasts occurred not far from a customs centre, but Mohammed denied the establishment was the target.
In Damaturu a bomb went off at a popular open air drinking spot where a locally-brewed gin is normally served in a suburb named Kandahar, according to a regular patron.
"There was a loud bang... which raised dust all over the place. This was followed by pandemonium as everybody took to their heels," Henry Samuel said by phone from Damaturu.
"So I can't say whether there were casualties or not because I ran off as soon as I heard the blast."
Another resident, Mamman Jika confirmed hearing an explosion coming from Kandahar.
In a first attack since the state of emergency was declared, but outside the areas covered by the decree, gunmen attacked a police station in northern Nigeria's Jigawa state, killing a teenage girl and wounding an officer late Tuesday.
"The gunmen shot indiscriminately into the police station and engaged our men in a shootout, killing a teenage girl trying to flee and wounding a policeman," Jigawa state police commissioner Hashimu Argungu said.
He said an explosive thrown into the police station failed to detonate.
No one claimed responsibility for the attack, though Boko Haram has been blamed for scores of such incidents.
A Damaturu hospital source said bodies of two civilians shot in a separate incident were brought in from an area on the outskirts of the city. It was not clear who shot them or why.
Jonathan's weekend declaration of a state of emergency in parts of four northern states hard hit by attacks blamed on Boko Haram, was in response to a wave of attacks attributed to the group.
While Boko Haram has been staging increasingly deadly attacks for months, including an August suicide bombing of UN headquarters in Abuja that left 25 dead, the Christmas bombings that killed 49 people as services ended at a Catholic church sparked intense fear and outrage.
Nigerian authorities said they did not believe militants would follow through on the ultimatum, but added that they were taking no chances.
Muslims have frequently been victims of Boko Haram attacks, most of which have occurred in northeastern Nigeria, but the Christmas Day bombings particularly targeting churches set off fears of retaliation from Christians.
Nigeria, Africa's largest oil producer and most populous nation with 160 million people, is roughly divided between a mainly Muslim north and predominantly Christian south.
Followers of the two faiths however co-exist with millions of Muslims based in the south and millions of Christians in the north.