Maiduguri — A female suicide bomber killed herself Monday when she exploded a vehicle packed with explosives near a stadium where Goodluck Jonathan had just held an election rally in Gombe, police said. They said there were no other casualties.
The U.S. State Department, meanwhile, published a warning urging U.S. citizens not to travel to 17 of the country's 36 states "due to the risk of kidnappings, robberies, and other armed attacks." The list encompasses every state in the far north, central Plateau state and Delta, Bayelsa and Rivers in the oil-rich south.
Monday's explosion occurred about 1.5 kilometers (1 mile) from the venue, which President Goodluck Jonathan had just left, said Deputy Superintendent Fwaje Atajiri.
Two other suicide bombings in Gombe city on Sunday injured a few people but killed only the bombers, he said. A couple sharing a bicycle blew themselves up at a central traffic circle and a man blew himself up at a timber market. All three bombers died, Atajiri said.
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No one immediately claimed responsibility. Most suicide bombings are blamed on Boko Haram extremists who are against democracy and have vowed to disrupt the February 14 elections for the president, state governors and legislators in Nigeria, Africa's richest and most populous nation.
The attacks come as the International Criminal Court prosecutor urged participants to refrain from violence before, during and after the vote, with analysts saying the presidential contest is too close to call.
Prosecutor Fatou Bensouda said she would send a team to Nigeria before the election, noting: "Experience has shown that electoral competition, when gone astray, can give rise to violence and in the worst-case scenarios, even trigger the commission of mass crimes that shock the conscience of humanity."
Front-runners are President Goodluck Jonathan, and Muhammadu Buhari, a former military dictator. Some 800 people died in protests in mainly Muslim northern Nigeria after Buhari lost the last election to Jonathan in 2011.
Prosecutors at The Hague-based court already are conducting a preliminary probe into alleged war crimes committed by Boko Haram and by Nigerian security forces that could lead to a full-blown investigation.