MAIDUGURI, Nigeria (Reuters) - A radical group attacked a police vehicle in northeastern Nigeria, killing seven people, in the latest in a string of attacks by the group in the last week, the military said on Thursday. A military spokesman said the Boko Haram group was behind the attack on Wednesday, in which the police vehicle was burned to ashes at a bus station in the Dala area of Maiduguri. Eight people were wounded. The group claimed responsibility for Christmas Eve bombings in the central Nigerian city of Jos which killed at least 80 people. Nine people died this week in two other Boko Haram attacks in Maiduguri, a city in one of Nigerias poorest regions near its northeastern borders with Cameroon, Chad and Niger. Jonathan can ill afford a security crisis, as any unrest in Africas most populous nation is likely to be used by his rivals to undermine his credibility. Going on previous Nigerian election cycles weve seen, there is often a strong political theme behind insurgent attacks, said Patrick Smith, editor of Africa Confidential. Whose interests do the attacks serve best? Clearly it benefits Jonathans opponents. Any unrest is going to make him look weak. Nigerian elections usually favour the incumbent and Jonathan is still the front runner, but his campaign is controversial. A party pact says that power within the ruling Peoples Democratic Party (PDP) should rotate between the mostly Muslim north and largely Christian south every two terms. YarAdua, a northerner, died during his first term, and some northern factions are opposed to the candidacy of Jonathan, a southerner. He faces a northern challenge from former Vice President Atiku Abubakar for the party nomination, and some fear any unrest will be used by rivals to undermine the incumbent. Hundreds of people died in religious and ethnic clashes at the start of the year in the countrys Middle Belt where the mostly Muslim north meets the predominantly Christian south. The tension is rooted in decades of resentment between indigenous groups, mostly Christian or animist, who are vying for control of fertile farmlands and economic and political power with migrants and settlers from the north. Nigeria is due to hold a presidential election on April 9, parliamentary elections on April 2, and voters will elect governors in the 36 states to round off the process on April 16.