Nigeria's president and vice president have both started legal proceedings in a dispute over whether the vice president can remain in office.
President Olusegun Obasanjo says Vice President Atiku Abubakar should not stay in office after accepting an opposition party's nomination to run in the presidential election next April. The president says the constitution stipulates that both the president and his deputy should belong to the same political party.
Vice President Abubakar says he has a right to remain in office until his term ends or unless he is impeached.
Both politicians on Wednesday asked an appellate court in the capital, Abuja, to rule on the issue.
The ruling People's Democratic Party expelled Abubakar last week and urged the president to dismiss him. The party suspended him earlier this year over corruption allegations. Abubakar says the charges are politically motivated.
Last week, Abubakar accepted the support of a small opposition party, the Action Congress, for his presidential candidacy.
Tensions have been growing for months between the vice president and President Obasanjo. Their relations soured after the vice president opposed an effort to amend the constitution so President Obasanjo could run for a third term.
Some information for this report was provided by AFP and AP.