Togolese opposition leader Agbeyome Kodjo said on Wednesday he has filed a suit to overturn the result of presidential elections in which he placed a distant second to incumbent Faure Gnassingbe.
"I filed a petition to the Constitutional Court on Tuesday evening," he told AFP.
"We expect the court to annul the false results published by CENI," the Independent National Electoral Commission, he said.
Kodjo, a former prime minister, won 18.37% of the vote on Saturday and Gnassingbe 72.36%, according to preliminary official results. Turnout was put at 76%.
The win, which had been widely expected, extended more than a half century of dynastic rule over the former French colony by the Gnassingbe family.
The opposition alleged widespread fraud including ballot stuffing and the use of fake polling stations to skew the outcome in Gnassingbe's favour.
Some 300 international observers were deployed, mainly from the Economic Community of West African States (Ecowas) and the African Union (AU), many of whose members supported Gnassingbe.
The Ecowas observers on Monday urged the candidates to "respect the results that have emerged from the ballot boxes and have been declared by the institutions" and resort to the courts to resolve any grievances.
The AU called on the Togolese public to "continue to work to preserve peace and stability, in order to consolidate democracy and the state of law."
Gnassingbe, 53, took the helm in 2005 after the death of his strongman father, Gnassingbe Eyadema, who seized power in a coup in 1967.
The small West African state has a poverty rate of around 50 percent and is ranked 167th of 189 countries on the UN's human development index.