BANJUL (Reuters) - Gambian President Yahya Jammeh’s ruling party challenged his defeat in a Dec. 1 election at the Supreme Court on Tuesday as West African leaders failed to reach a deal that would see him accept the result and end a deepening political crisis.

Gambian President Yahya Jammeh attends a meeting with a delegation of West African leaders during the election crisis mediation at the presidential palace in Banjul, Gambia December 13, 2016. REUTERS/Stringer

Soldiers also seized the headquarters of the national elections commission and sealed it off just hours before the mediation delegation representing regional bloc ECOWAS touched down in the tiny riverside nation.

Jammeh, who has ruled Gambia since taking power in a 1994 coup and is accused of widespread rights abuses, initially conceded defeat to his main challenger, Adama Barrow. But in a dramatic about-face that drew international condemnation he then rejected the poll results last Friday.

The legal petition filed by the Alliance for Patriotic Reorientation and Construction now raises the prospect that Barrow’s narrow victory, which was poised to end years of Jammeh’s autocratic rule, may be overturned.

“The petition prays that it be determined that the said Adama Barrow was not duly elected or returned as president and that the said election was void,” read the text of the document submitted to the court and seen by Reuters.

Liberian President Ellen Johnson Sirleaf, a Nobel peace laureate, led the ECOWAS delegation that also included Nigeria’s Muhammadu Buhari, Sierra Leone’s Ernest Bai Koroma and Ghana’s John Mahama, who lost an election last week and conceded defeat.

“It is not time for a deal. It is not something that can happen in one day. It is something that we have to work on,” Johnson Sirleaf said as the presidents prepared to leave Gambia.

Regional leaders will discuss the crisis at an ECOWAS summit in Nigeria on Saturday, she said, adding Jammeh had given her assurances that peace and stability would be preserved.

But in an apparent sign that Jammeh was further entrenching his position, security forces seized control of the Independent Electoral Commission headquarters, which holds the original poll records.

“The military came to my office and said I am not to touch anything and told me to leave,” said commission chairman Alieu Momarr Njai. “I am worried for my safety.”

“STANDOFF”

Barrow, who received the unified backing of Gambia’s opposition in the election, has vowed to reverse Jammeh’s most capricious decisions, including a recently announced withdrawal from the International Criminal Court.

“I think everyone knows the issue here. There is a standoff between the government and our side,” Barrow said after meeting the regional heads of state.

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If negotiations fail, diplomats say, Gambia’s neighbors might consider removing him by force. Marcel de Souza, head of the ECOWAS commission, told Radio France International on Monday that sending troops was “a conceivable solution”.

Gambia’s president officially has 60 days to hand over power, but his move to challenge the result at the Supreme Court - the legal channel for resolving poll disputes - could put the international community in a difficult position.

Rights groups say Jammeh exerts strong influence over the court, which has not held a session for a year and a half. Legal experts believe that at least four new judges would need to be hired to hear his petition.

With Gambian judges no longer willing to serve on the Supreme Court, foreign judges have increasingly been brought in to hear cases. The current chief justice is from Nigeria.

The role of Gambia’s army will now be critical and the United States said on Monday some military officers had sided with Jammeh.

Army chief General Ousman Badjie had previously called Barrow to pledge his allegiance, the latter’s spokeswoman said. But Badjie’s support for the president-elect appeared far less certain on Tuesday.

“I support the commander in chief, whoever it may be. I support the commander in chief Jammeh,” Badjie told Reuters.

Barrow, who has no official state security detail, said in an interview on Monday he was concerned for his own safety.