Malaysia's highest court upheld a sodomy conviction for Opposition Leader Anwar Ibrahim on Tuesday, a ruling both critics and Anwar denounced as a "political conspiracy," USA Today reported.

Ibrahim, who also served as deputy prime minister, was first acquitted of the sodomy charge for allegedly having sex with a male political aide in 2008. But an appeals court in the mostly Muslim country, where sodomy is outlawed, overturned the verdict in 2014.

Ibrahim, who has a previous sodomy conviction, filed a last appeal with the top court in Malaysia's federal Putrajaya district, but his conviction was upheld after the court cited "overwhelming evidence" he had sex with the former aide, USA Today reported.

"In bowing to the dictates of your political masters, you have become partners to the crime," and "chosen to be on the dark side," 67-year-old Ibrahim told the panel of judges, surrounded by his wife and kids, the Agence France-Presse reported.

"I will not be silenced!" he added. "I will never surrender!"

Ibrahim rose to popularity as the opposition leader to the UMNO party, which has ruled the nation's political land for 60 years, according to USA Today. He won the popular vote in 2013's national elections but did not garner a majority of seats for parliament.

He served a six-year sentence for a 2004 sodomy conviction, which Al Gore, then U.S. vice president, also criticized as politically-motivated.

"Allowing this travesty of justice to stand will further undermine respect for rights and democracy in Malaysia," Phil Robertson, Asia director for Human Rights Watch, told USA Today.

Malaysian Prime Minister Najib Razak, however, stood by Tuesday's ruling.

"Malaysia has an independent judiciary, and there have been many rulings against senior government figures," his office said.

Ibrahim is to serve a five-year sentence, which disqualifies him from office and from participating in the 2018 elections.

"We call on all parties involved to respect the legal process and the judgment."