He was arrested on Wednesday and questioned for eight hours over the case. He was not formally charged, but police say he remains a suspect in the case.

Speaking to reporters Anwar said he was treated like a "major criminal" and needed medical treatment after a night in a bare cell at Kuala Lumpur police headquarters which aggravated a back injury.

"Dumped in a cell to sleep on a cold cement floor with nothing... that has exacerbated the pain," he said.

He added that he was subjected to an examination which included the measuring of his genitals.

"They have seen all my private parts. Of course I refused to be photographed, it could be on YouTube very soon! You mean I can trust the system?"

'Vengeance'

Anwar supporters gathered outside police headquarters to protest his arrest [EPA]
He described his arrest on Wednesday and his detention overnight as "absolutely unnecessary" saying the police actions were "an act of personal vengeance" against him.

Police officials have said he received fair treatment during his almost 24 hours in custody during which he was allowed two visits by family members.

Speaking to Al Jazeera Syed Hamid Albar, the Malaysian home affairs minister, denied that there were any political motivations in the case, saying it was a purely criminal investigation.

"There is no political motivation for us to bring a case just because we fear we are under political threat by him – I don't think we fear that," he said.

Anwar was arrested an hour before a police deadline for him to voluntarily answer charges that he sexually assaulted a young male aide, the second time he has faced sodomy accusations in a decade.

He has described the sodomy allegations as a "fabrication" and a "malicious" attack by his political enemies.
 
Sodomy is illegal in Malaysia and carries a jail sentence of up to 20 years if convicted.

US concerns

Responding to news of Anwar's arrest on Wednesday the US State Department said the case raised "serious questions and concerns" over the rule of law in Malaysia.
 
"We urge Malaysian authorities to resolve this matter in a manner that builds confidence in the impartial rule of law in Malaysia," Sean McCormack, a department spokesman, said in a statement.
 
In 1998 Anwar faced similar charges when he was accused of sodomising a male assistant.
 
The accusation led to his sacking from his posts as finance minister and deputy prime minister and an eventual jail sentence, sparking massive street protests by supporters.
 
His conviction on sodomy charges was later overturned by Malaysia's high court, but he served six years on a related corruption charge.

Anwar has said repeatedly that both charges were trumped up by political opponents and the police.

With the Anwar case once again stirring political tensions in Malaysia, police have implemented road blocks and security checks around Kuala Lumpur in an effort to prevent fresh protests.