YAOUNDE, Cameroon (AP) — Cameroon’s constitutional council on Tuesday rejected opposition candidate Maurice Kamto’s appeal to be reinstated on the ballot for the upcoming presidential election.

Kamto, a former government minister, is seen as the main challenger to long-serving President Paul Biya. Kamto had filed an appeal last month after the electoral commission did not include him in the list of approved candidates.

The decision Tuesday fueled fears of unrest and increases the likelihood of another Biya victory.

Security forces were deployed around the conference center in the capital Yaounde, where the Constitutional Council announced the verdict, and along the city’s major roads.

The previous day, police had fired tear gas and arrested dozens of people who were protesting in support of Kamto ahead of verdict.

Kamto was considered Biya’s strongest rival in past elections. He came second during the last presidential election in 2018 with 14% of the vote, while Biya cruised to victory with over 70% in an election marred by irregularities and a low turnout.

Biya, 92, the world’s oldest serving head of state, said last month he would seek reelection on Oct. 12 despite rumors that his health is failing. He has been in power since 1982, nearly half his lifetime.

Biya’s rule has left a lasting impact on Cameroon. His government has faced various challenges, including allegations of corruption and a deadly secessionist conflict in the nation’s English-speaking provinces that has forced thousands out of school.