Image copyright AFP Image caption The protesters say that last weekend's election results were tainted by massive fraud

Thousands of Malaysian opposition supporters have rallied against alleged fraud in the election, defying police who said the protest was illegal.

Opposition leader Anwar Ibrahim called the protest after what he said were "stolen" polls, won by PM Najib Razak's ruling coalition.

Mr Najib's Barisan Nasional (BN or National Front) coalition won 133 of the 222 parliamentary seats on Sunday.

It was the coalition's worst result in more than half a century in power.

While it secured a simple majority, it failed to regain the two-thirds parliamentary majority it lost for the first time in 2008.

The BN has vehemently denied the opposition's allegations of cheating and accused Mr Anwar of deliberately choosing a small stadium on the outskirts of the capital Kuala Lumpur for the rally to ensure it would spill onto the streets.

But the three-party opposition alliance - which mounted its strongest-ever challenge to the coalition - has called for a recount.

Up to 40,000 protesters, many dressed in mourning black, gathered at the demonstration to denounce the results. Participants filled the stadium's stands and spilled onto the football field.

They complain that indelible ink - meant to prevent multiple voting - could be easily washed off and that accounts abound of a government scheme to fly tens of thousands of "dubious" - and possibly foreign - voters to flood key constituencies.

The United States has also raised questions about the conduct of the election, with the White House urging the government to address concerns.

'Fierce movement'

Mr Anwar called on his supporters to gather at Kelana Jaya Stadium at 20:30 local time (12:30 GMT) on Wednesday.

Malaysia 2013 polls Election was considered Malaysia's most keenly contested poll since independence

PM Najib Razak leads the long-dominant coalition Barisan Nasional (National Front)

Anwar Ibrahim leads the three-party opposition coalition Pakatan Rakyat

Key poll issues included corruption, race-based policies that favour ethnic Malays, and the economy

Turnout was estimated at a record 80%, election officials said

In 2008, of the 222 seats in parliament the BN won 140 and the opposition won 82

In 2013, the BN won 133 seats and the opposition 89 Profile: Najib Razak Profile: Anwar Ibrahim

"This shall be a beginning for a fierce movement to clean this country from election malpractice and fraud, for there is no opportunity for renewal without a clean and fair elections," Mr Anwar had told Reuters news agency on Tuesday.

"Enough of this oppression. Please for once, for once, see the change in the mood of the people."

But National Police Chief Ismail Omar told state news agency Bernama on Tuesday the protest was illegal because organisers did not have a permit.

But Tian Chua, spokesman for the opposition, said the protest was lawful.

"Strictly speaking, the police do not have the power to ban a rally which is held within a stadium," he told Radio Australia.

He added that under the law, people have the right to hold a peaceful gathering if the owners of the venue agree.

The government has insisted that the 5 May polls were free and fair, and say that evidence of fraud should be presented.

However, the independent Institute for Democracy and Economic Affairs (Ideas) and the Centre for Public Policy Studies (CCPS) watchdogs have said there were "serious flaws".

"Having conducted an independent and impartial observation of the elections, Ideas and CPPS conclude that [the election] was only partially free and not fair," its joint report said.

Irregularities included questions over campaign spending and the Election Commission's independence from the government coalition.

The watchdogs also cited inequalities in how the constituencies were demarcated.