Malaysian opposition leader Anwar Ibrahim said he was the victim of a "political conspiracy" on Tuesday as the nation's highest court sent him to jail for five years on a sodomy conviction that will likely end his career.
Anwar had challenged a conviction handed down last year for sodomising a young male former aide, but the Federal Court struck down his appeal, saying there was "overwhelming evidence" of the crime.
The decision was sharply criticised by the United States, Australia and human rights organisations.
Sodomy is punishable by up to 20 years in prison in Muslim-majority Malaysia. Anwar was taken from the court in the afternoon to begin his sentence.
Shortly after the decision was announced, Anwar took to the dock to launch a scathing attack on the justices, accusing them of collusion in a "political conspiracy" by Malaysia's authoritarian regime.
"In bowing to the dictates of your political masters, you have become partners to the crime," he said.
"You have chosen to be on the dark side."
"I will not be silenced! I will never surrender!" Anwar shouted at the judges as they abruptly got up to leave.
Government critics call the case part of a long-running campaign to destroy Anwar, a former deputy premier who was ousted from the ruling party in the late 1990s and later helped unite a previously divided and hapless opposition into a formidable force.
The ruling is a heavy blow to both Anwar and the opposition.
Anwar is now 67. Even if freed early, he is barred from politics for five years after his release, making another comeback unlikely.
"This is a struggle. Not only for Anwar but for all Malaysians, against a regime that will stoop to anything for political gain," Wan Azizah Wan Ismail, Anwar's wife and president of his political party, told local media.
Malaysian Prime Minister Najib Razak has previously admitted meeting Anwar's accuser, Mohamad Saiful Bukhari Azlan, in 2008 just before the charges were filed, but denies orchestrating the case.
A statement by his office insisted the court reached the verdict "only after considering all the evidence in a balanced and objective manner," and called on all parties to respect the decision.
But the ruling drew harsh criticism.
A US embassy statement said "the United States is deeply disappointed and concerned," adding that the episode "raised serious concerns regarding the rule of law and the independence of the courts."
Australian Foreign Minister Julie Bishop said her government was "deeply concerned by the severity of the sentence."
Amnesty International called it "deplorable" and part of a Malaysian government campaign to silence critics.
"We consider Anwar Ibrahim to be a prisoner of conscience," it said.
It is the second disputed sodomy conviction for Anwar in a career marked by sharp ups and downs.
He was a popular top leader of the ruling United Malays National Organisation (UMNO) until his ouster in a bitter 1998 power struggle that saw him arrested and jailed for six years on previous sodomy and corruption charges.
That case was widely viewed as tainted by politics, and the sodomy conviction was eventually thrown out.
Later joining the opposition, Anwar led a three-party alliance to the brink of ousting UMNO, one of the world's longest-ruling parties.
But the alliance risks falling apart over deep policy and personality differences. Sidelining Anwar raises troubling new questions, especially with no clear successor in the wings.
Analysts, however, say jailing Anwar also bears risks for Najib's regime, which lost the popular vote in 2013 elections, but clung to power through gerrymandering.
"Jail time will make Anwar a martyr for a new generation, rally his supporters at home and abroad and signal the weakness of (Najib's) government in its need to remove an opponent," Bridget Welsh, a Southeast Asia politics analyst with National Taiwan University, wrote in a recent essay.
UMNO has a history of using police and judicial organs to pressure opponents.
The current charges were filed in 2008 shortly after the first of two historic Anwar-led opposition election showings.
Many legal experts had expected Anwar's acquittal, but Chief Justice Arifin Zakaria said in reading out the court's judgement that it found Saiful's accusations "credible".
"We have overwhelming evidence that (Saiful) was sodomised," he said, adding that Anwar's conspiracy allegations "remain unsubstantiated".
UMNO has dominated multi-ethnic Malaysia since independence in 1957, but has rapidly lost ground to the opposition Pakatan Rakyat (People's Pact) alliance, which vows to dismantle UMNO's authoritarian rule and crony capitalism, and to reform discriminatory policies favouring the ethnic Malay majority.