DAKAR, Senegal (AP) — Nigeria's president was leading a regional delegation to Gambia in a last-ditch attempt Friday to persuade its longtime leader to step down and allow his rival's inauguration next week, while fears grow that the impasse could turn violent.

President Muhammadu Buhari has been authorized to offer Gambian President Yahya Jammeh asylum, if necessary, during the visit.

The West African regional bloc also has a military force on standby to intervene if Jammeh does not step down when his mandate expires Jan. 19.

Jammeh at first accepted his Dec. 1 election loss, even making a telephone call to concede on national television, but then changed his mind and declared that "only Allah" can deny him victory. His party is now contesting the results in court.

President-elect Adama Barrow is renewing his offer to Jammeh for direct discussions on the crisis, telling the BBC that "I'll be very willing to talk to him directly."

The court challenge to the election results shows complications. Gambia's Supreme Court, short of judges, has said it might not be able to consider the challenge until May, and Jammeh says Gambia should await its decision.

Jammeh took power in a coup in 1994 and is accused of gross rights violations including arbitrary detentions, torture and the killings of opponents in this tiny country of 1.9 million people that is nearly surrounded by Senegal.

Jammeh might be wary of a Nigerian promise of safe haven. Nigeria offered asylum to Liberian warlord Charles Taylor in 2003 to help end the civil war he started in 1989, but it was forced by international pressure to hand Taylor over in 2006 for trial for war crimes committed in Sierra Leone. Taylor was convicted in 2013 and is serving a 50-year sentence in a British prison.