( L - R ) Abubakar and Obasanjo

LAGOS, (Reuters):

Nigeria's president and vice president have taken their fight for political supremacy to the courts by seeking a ruling on whether the latter's defection to an opposition party amounts to a resignation.

The escalating feud in the run-up to elections in April has tainted the reputations of both men, and lawmakers are considering the possibility of impeaching them both in the wake of mutual accusations of corruption.

President Olusegun Obasanjo said last week Vice President Atiku Abubakar had "technically resigned" by joining the opposition Action Congress and he had removed all Abubakar's privileges of office while he sought a replacement.

Abubakar called the move a coup against the constitution and filed a case on Wednesday evening asking the appeals court to clarify the legal position.

Obasanjo filed a counter-case asking the same court to stop Abubakar "parading himself" as the vice president of Nigeria, Africa's top oil producer and most populous nation.

"Now that both sides are in court, this dispute can be resolved judicially once and for all. I hope both sides abide by the judgment of the court because it has threatened the security of the country," said Femi Falana, a top human rights lawyer.

The constitution says the vice president should be from the same party as the president at the time of election, but it makes no provision for a subsequent defection.