A car bombing near a church in the northern Nigerian city of Kaduna on Easter Sunday killed at least 20 people, while another blast later in a separate city caused a number of injuries.
The deadly explosion in Kaduna, an important cultural and economic centre in Nigeria's north, was a stark reminder of Christmas Day attacks that left dozens of people dead in Africa's most populous nation and largest oil producer.
Motorcycle taxi drivers and residents who had stopped at a stall in the area to buy tea appeared to have borne the brunt of the blast, and body parts littered the area.
As news of the attack early Sunday spread, security forces boosted patrols in key areas, including in the capital Abuja, where soldiers were sent to reinforce police posted near churches, an AFP correspondent reported.
There was no immediate claim of responsibility.
At least one car said to be driven by a suicide bomber was believed to be involved. A rescue official speaking on condition of anonymity said two vehicles packed with explosives detonated.
"Now we have 20 dead from the twin explosions," the rescue official, who was not authorised to speak publicly, told AFP. "Bombs concealed in two cars went off just opposite this church."
Police later confirmed the death toll of 20 and said 30 others had been wounded.
A police officer at the scene said a man believed to be a suicide bomber driving a car had been stopped at a checkpoint near the Evangelical Church of West Africa, and had turned back.
He then drove to a nearby area in front of a hotel, close to the Assemblies of God church, and detonated the bomb. The church did not appear to have significant damage, but a third church nearby reported having windows broken.
Services were ongoing at the churches at the time of the blast, but worshippers did not appear to have been affected. Other cars in the area were damaged, but it was unclear if they were also carrying explosives, police at the scene said.
A spokesman for the national emergency management agency said most of the victims appeared to be motorcycle taxi drivers. One resident said the explosion was strong enough to shake his house and cause his ceiling to cave in.
Late Sunday, another bomb blast rocked an area of the central Nigerian city of Jos, with an emergency spokesman reporting a number of injuries. Police confirmed one person wounded from the bomb, which had been left in a bag near the roadside.
Separately in the northeastern city of Maiduguri, soldiers raided a suspected hideout for members of Islamist group Boko Haram and killed three gunmen they blamed for a recent market shooting that left seven traders dead, an army spokesman said.
The raid in Maiduguri, traditionally Boko Haram's base, was not believed to be directly linked to either of the bombings. Two people were also arrested in the raid, the spokesman said.
Boko Haram carried out a series of attacks on churches and other locations on Christmas day, the bloodiest at a church outside Abuja, where 44 people died.
The Nigerian authorities as well as foreign embassies had warned of the possibility of an attack on Easter Sunday.
Boko Haram's increasingly bloody insurgency has left more than 1,000 people dead since mid-2009. Police and soldiers have often been the victims of such attacks, though Christians have been targeted as well.
Sunday's bombing came as Pope Benedict XVI condemned "savage terrorist attacks" against churches in Nigeria as part of his Easter message.
Boko Haram also claimed responsibility for the August suicide bombing of UN headquarters in the capital Abuja which killed 25 people.
Its deadliest attack yet occurred in the northern city of Kano on January 20, when coordinated bombings and shootings claimed at least 185 lives.
An attempt to hold indirect talks between Boko Haram and the government last month appears to have collapsed, with a mediator quitting over leaks to the media and a spokesman for the Islamists saying they could not trust the government.
There has been intense speculation over whether Boko Haram has links to outside extremist groups such as Al-Qaeda's north African branch.
Diplomats say such links so far appear limited to training for some Boko Haram members in northern Mali with Al-Qaeda elements, without significant evidence of operational ties.
Analysts say deep poverty and frustration in Nigeria's north has fed the violence, pushing young people toward extremism.
Nigeria's 160 million population is roughly divided between a mainly Muslim north and predominately Christian south.