Supporters of the "Bersih" electoral reform coalition are ushered into a police truck near the National Museum after being detained before a planned Bersih rally in Kuala Lumpur July 9, 2011. [Photo/Agencies]

KUALA LUMPUR - Police fired tear gas and detained hundreds of activists as more than 20,000 demonstrators massed Saturday across Malaysia's main city demanding electoral reforms in the country's biggest political rally in years.

The opposition-backed rally was the culmination of weeks of intense pressure on Prime Minister Najib Razak's long-ruling coalition to make election laws fairer and more transparent ahead of national polls widely expected by mid-2012.

Demonstrators marched in defiance of Najib's administration, which declared the rally illegal and warned people repeatedly to avoid it. Officials insisted it was merely an opposition attempt to trigger chaos and stir anti-government sentiment, while activists accused authorities of being afraid of any large display of dissent that could undermine their authority.

Authorities took extraordinary security measures to deter Saturday's rally by sealing off roads, closing train stations and deploying trucks with water cannons near the Independence Stadium in downtown Kuala Lumpur where activists sought to gather.

Police said in a statement that they detained 1,667 people in a clampdown called "Operation Erase Bersih," referring to the Bersih coalition of civic groups that organized the rally. Those arrested included several senior opposition officials. Some were released after several hours, with police indicating that most would not be held overnight.

Thousands tried to reach the stadium from various parts of Kuala Lumpur, chanting "Long live the people" and carrying yellow balloons and flowers as they marched.

Police fired numerous rounds of tear gas and chemical-laced water in repeated attempts to disperse the crowds, causing demonstrators to scatter into nearby buildings and alleys before they regrouped. Police helicopters flew overhead as a brief downpour failed to deter the protesters.

The demonstrators dispersed after a five-hour standoff with police. Only several hundred reached the stadium.

Najib insisted Saturday the protesters only represent a minority, and that most Malaysians support his administration.

"If there are people who want to hold the illegal rally, there are even more who are against their plan," the prime minister was quoted as saying by the national news agency, Bernama.

Witnesses said riot police armed with batons charged at some protesters and dragged them into trucks. Some were seen bleeding, but police could not confirm any injuries.

Anwar Ibrahim, Malaysia's top opposition figure, said on Twitter that he sustained a "minor injury" when his group was hit by tear gas. The Malaysiakini news website said he had a knee injury.

The crackdown "stirred a sense of outrage against the exhibition of raw power by our government," Bersih coalition leader Ambiga Sreenavasan told reporters.

"What is the necessity for a show of might against right? No matter what, right will always prevail," she said, minutes before police detained her and other Bersih officials as they walked to the stadium.

Organizers said 50,000 took part in the rally, but police claimed there were only up to 6,000. Other observers and participants said the total was between 20,000 and 30,000, noting that it was highly unlikely that police could have arrested a quarter of the demonstrators. An accurate count was impossible because they were scattered in various areas.

The rally has galvanized the opposition and has been credited for a surge in political awareness among the public in recent weeks.

Opposition leaders accuse Najib's National Front coalition of relying on fraud to preserve its 54-year grip on power, which has been eroded in recent years amid mounting complaints about corruption and racial discrimination. The government insists the current electoral policies are evenhanded.

The activists' demands include an overhaul of voter registration lists, tougher measures to curb fraud and fairer opportunities for opposition politicians to campaign in government-linked media. The National Front's mandate expires in mid-2013 but many analysts expect elections to be called by next year.

Supporters of the Bersih coalition were also planning solidarity marches over the weekend in foreign cities, including in Australia, Britain, France, Hong Kong, Indonesia, Japan, the Philippines, South Korea, Thailand and the United States.

In Washington, State Department spokeswoman Victoria Nuland said the US has been communicating to Malaysia the importance of respecting human rights, including freedom of expression and assembly.

"We consider it incumbent on all sides to refrain from violence," she told a news conference Friday.

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"We are not criminals, we are just asking for free and fair elections," opposition leader Anwar Ibrahim's daughter, Nurul Izzah Anwar, told reporters after her father was knocked down and hurt in a melee when he and his supporters were tear gassed.

"Many innocent people were injured. We condemn this act of cruelty by UMNO and Barisan Nasional," she said, referring to Najib's party and the ruling coalition.

Street protests are rare in this Southeast Asian nation, but foreign investors are worried that any groundswell of anti-government sentiment could delay economic reforms seen as essential to draw investment.

If he is put under popular pressure, Najib may reconsider plans for a snap election and hold back on reforms such as cutting fuel subsidies or unwinding an affirmative action programme for the country's Malay majority.

Polls are not due until 2013 but analysts have said Najib could seek an early mandate after economic growth accelerated to a 10-year high in 2010.

"From Najib's perspective, holding elections anytime soon would be a mistake because of the damage that has been done today," said Bridget Welsh, Malaysia specialist at Singapore Management University.

"The fact that such a large crowd turned up despite a crackdown shows that voter anger is deep and this is going to push a lot of people who are in the middle towards the opposition."

Reuters witnesses saw tear gas shells lobbed repeatedly at groups of protesters in downtown Kuala Lumpur as the crowds chanted "Long Live the People" and "Reformasi, reformasi," the Malay word for reform.

"We have made our point that we want free and fair elections," said Chan Mei Yin, a 32-year old accountant who joined the protest.

"The police are just showing that they are brutal to Malaysians. I will not vote for this government."

NOT THAILAND

While Malaysia is far from being divided by political strife like its northern neighbour Thailand, the opposition has been steadily growing more vocal.

Tens of thousands of demonstrators took to the streets at a November 2007 rally, which analysts said galvanised support for the opposition ahead of record gains in a 2008 general election.

Analysts said the turnout of protesters on Saturday was more than 10,000, around the same as in 2007. Police, however, put the number at 5,000-6,000, while protest organisers claimed 50,000 attended.

"Malaysian civil society is showing the government that intimidation will not work," said Ooi Kee Beng, a political analyst at the Institute of Southeast Asian Studies of Singapore.

"We're seeing a lack of will on the part of the government to try to negotiate and to defuse the situation. It's all going to look very bad outside Malaysia."

After Malaysia's constitutional monarch tried to defuse the situation, the government initially offered Bersih (Clean), the group that called the protest, the use of a stadium to hold its demonstration.

But it baulked at allowing the group to use the main stadium in downtown Kuala Lumpur, at which point Bersih said it would defy the ban.

From midnight, police locked down the central shopping district of the city of 1.6 million people, setting up roadblocks and barring taxis and buses from the area. Suburban trains, however, continued to operate and other areas of the city were not affected.

Bersih has vowed to bring together tens of thousands of supporters to the protest but it fell short. Still, some analysts said the government faced a problem.

"Just looking at the crowd there were many 'first timers', young people from the Facebook generation who just wanted to have a peaceful life," said Ibrahim Suffian, director of the independent opinion polling outfit Merdeka Center.

"This is trouble for Najib as it will polarise traditionally non-political segments of society like the young even further away from him."

Najib took power in 2009, and inherited a divided ruling coalition which had been weakened by historic losses in the 2008 polls. He has promised to restructure government and economy and introduced an inclusive brand of politics aimed at uniting the country's different races.

Najib's approval ratings have risen from 45 percent to 69 percent in February, according to independent polling outfit Merdeka Center. But analysts said recent ethnic and religious differences have undermined his popularity.