Malaysian opposition leader Anwar Ibrahim has vowed to seize power from a "corrupt" government at a rally of some 15,000 supporters as he fights back against new sodomy accusations.

In an impassioned speech to a packed stadium Tuesday night, Anwar said it was time to boot out the Barisan Nasional (BN) coalition which has governed Malaysia for a half a century since independence from Britain.

"The BN government cannot be trusted to manage the economy of this country because there is too much corruption," he told the crowd which shouted the opposition battle cry of "Reformasi" or "Reform".

"Time is up, you get out, let us move in!" Anwar said to loud cheers.

Anwar, a former deputy premier who was sacked a decade ago and spent six years in prison n sodomy and corruption counts, made a stunning return to politics in March elections that dealt the BN an unprecedented setback.

The 60-year-old political maverick said the new accusations of sexual assault by a 23-year-old male aide who volunteered in his office for several months "never happened".

"I will fight these allegations day and night and I won't accept defeat over this evil and lies," he said, adding that his accuser was being manipulated by powerful forces.

"He just became a pawn in their game to attack me. I'm sad that the young boy has ended up in this way." Sodomy is a criminal offence in this conservative country which is predominantly Muslim.

Anwar has said he is poised to form a government with the help of defecting lawmakers from the ruling coalition, putting intense pressure on Prime Minister Abdullah Ahmad Badawi who faces calls to quit over the polls debacle.

"They are still in a state of denial now that we have wrested so much power from them," Anwar told the crowd, adding he had evidence that the government was mounting a conspiracy to humiliate him.

"Do you think I am going to be quit? We will fight them."

The stadium in suburban Kuala Lumpur was decorated with posters showing Anwar with a black eye, inflicted in a severe beating by the police chief shortly after his sacking.

"Don't let this happen again," read the caption.

Anwar fled to the Turkish embassy on the weekend, saying he feared for his life after being informed he could be targeted with a government assassination attempt.

He left his refuge on Monday after the government guaranteed his safety, but precautions were tight at the rally and Anwar was led into the hall by a line of security personnel.

He addressed the crowd from a stand that was separated from the crowd by metal barricades, and with a long line of party security personnel lining its perimeter.

Anwar also took aim at the government's unpopular 41 per cent fuel price hike this month, and invited the crowd to take part in a mass anti-inflation rally on July 6 which organisers hope will attract one million people.

"I promise that the day we take power, the very next day oil prices will drop in Malaysia," he said.

His supporters in the crowd said their faith in the charismatic leader was not shaken by the new scandal.

"All these allegations against Anwar are false and the government is grasping at straws to try and destroy him, but this will not work," said Adlin Syufikah Ismail.

"The people are 100 per cent behind Anwar," said the 31-year-old marketing executive, dressed in a blue headscarf and traditional flowing dress.

Jamari Iskandar Shah, a 48-year-old salesman who attended the rally with his wife and two young children, was one of many who said they believed Anwar will be Malaysia's next prime minister.

"I brought my family so that they could learn the truth about what is happening in this country and so they will know why we need a new government in power," Jamari said.

"The people are suffering and yet politicians remain rich. This must change and the people must again be the priority and not cronies."