Senegal's new President Bassirou Diomaye Faye on Tuesday appointed firebrand politician and key backer Ousmane Sonko as prime minister in his first act as president, Reuters reports.

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Sonko, an opponent of former president Macky Sall, is popular among the country's youth but was barred from the March 24 presidential election due to a defamation conviction. He denied any wrongdoing.

Campaigning jointly under the slogan "Diomaye is Sonko," Sonko urged supporters to vote for his top lieutenant, Faye, who ultimately won with over 54 percent of the vote in the first round.

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Faye was inaugurated on Tuesday.

Speaking after his appointment, Sonko said he would present Faye with a full list of proposed ministerial appointments for his approval.

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"There will be no question of leaving him (Faye) alone to assume this heavy responsibility", Sonko said.