Anwar Ibrahim vowed Tuesday his Malaysian opposition would soon present evidence of government cheating in bitterly fought weekend elections as he called for a "fierce" campaign for electoral reform.
Anwar insisted his three-party Pakatan Rakyat (People's Pact) alliance would not back down from its insistence that victory was stolen from it last Sunday, setting the stage for an extended battle with the government for public opinion.
"In the next few weeks, we will present to the public proof that (Prime Minister Najib Razak) won this election through fraud and irregularities," he told reporters.
He also said a rally he plans to lead Wednesday night in a stadium outside the capital Kuala Lumpur would kick off a campaign for election reform.
"This shall be a beginning for a fierce movement to clean this country from election malpractices and fraud, for there is no opportunity for renewal without a clean and fair election," said Anwar, 65.
Najib was sworn in on Monday, a day after his Barisan Nasional (National Front) coalition retained its 56-year grip on power in elections touted as offering the first real chance of government change in history.
The coalition has governed since independence in 1957. It won with less then half the popular vote, thanks to self-serving redistricting over the years.
But Anwar has angrily refused to concede defeat, citing widespread reports of irregularities.
Voters across the country complained after the vote that indelible ink, touted by Najib as the cornerstone of his pledge of free and fair elections, was easily washed off.
Before the polls, Anwar had alleged a government scheme to fly tens of thousands of "dubious" and possibly foreign voters to sway the outcome in key constituencies, which Najib's office has denied.
But videos, pictures and first-hand accounts of purportedly foreign "voters" being confronted at polling centres by angry citizens have gone viral online.
A statement from Najib's office on Tuesday referred to such allegations as "unsubstantiated".
It remains unclear how extensive the response to Anwar's calls for a public movement will be, but clean-election activists have in the past two years brought tens of thousands into the streets for demonstrations demanding reform.
One of those, in 2011, prompted an embarrassed Najib to promise to look into the concerns. He appointed a panel which, among other things, suggested use of the ink, which is applied to a voter's finger to prevent multiple-voting.
The ink was supposed to be unwashable for a week.
Najib has brushed off Anwar's accusations as sour grapes, but has not explained the ink failure or disproven the other allegations, instead calling for "reconciliation" after the bitter elections.
Anwar called on participants in Wednesday night's rally to wear black in protest.
Anwar was Barisan's heir-apparent until his ouster in a 1998 power struggle with then-premier Mahathir Mohamad, which saw Anwar jailed for six years on sex charges widely viewed as trumped up.
Anwar later brought his pan-racial appeal to the once-divided opposition, dramatically reversing its fortunes with pledges to combat corruption and reform controversial affirmative-action policies for majority Malays.
Anwar had said he would step aside as opposition leader if it failed to take power, but said Tuesday that plan was on hold in light of the disputed election.
"The context (to step down) was in a free and fair election," he said.
But he added: "I now will continue the fight to defend the rights of all Malaysians."