The President confirmed his arrival in Banjul in a tweet.

The trip to Gambia is President Mahama's first foreign trip since losing Ghana's general elections to the New Patriotic Party's Nana Akufo-Addo last Friday.

He is part of a delegation headed by the chairperson of the Economic Community of West African States (ECOWAS) and Liberian leader, Ellen Johnson Sirleaf, Nigerian President Muhammadu Buhari and Sierra Leonian President Ernest Bai Koroma.

The West African leaders hope to persuade the incumbent Jammeh to agree to leave office after he lost the presidential elections.

Initially, Jammeh conceded defeat to Barrow sparking celebrations across the country but changed his mind a couple of days later citing "serious and unacceptable abnormalities" and calling for fresh polls.

In a televised statement late Saturday, Jammeh's Alliance for Patriotic Reorientation and Construction (APRC) party said it was preparing a petition "against the flawed decision of the Independent Elections Commission".

The deadline for submitting a challenge to the court is Tuesday.

Barrow is due on Tuesday to welcome the ECOWAS leaders along with a delegation of UN representatives, which the president-elect said gave him hope that he would soon take power.

Sirleaf said over the weekend that the reversal of Jammeh's decision "threatened peace".

She asked him on Saturday to "do the right thing and take actions to facilitate a smooth and peaceful transition in Gambia".

Background

Jammeh seized power in a coup in 1994 when he was an army lieutenant and has ruled ever since, wining four elections, that were criticised by rights monitors, and surviving several coup attempts. International human rights groups accuse him of widespread violations and repression.

He declared Gambia an Islamic Republic last year.

A statement from the opposition coalition read to reporters in Barrow's presence on Monday called for Jammeh to step down immediately.

Before his surprise change of mind, he had pledged to hand over power to Barrow in January following the transitional period dictated by Gambian law.

However, Gambia has no sitting Supreme Court. In order to hear Jammeh's complaint, legal experts believe at least four judges must be hired.