KUALA LUMPUR (Reuters) - Tens of thousands of protesters, undeterred by the arrests of opposition leaders, marched in Malaysia’s capital on Saturday demanding that Prime Minister Najib Razak step down.

Former Malaysian prime minister Mahathir Mohammad arrives to speak at a rally to pro-democracy group Bersih during a 1MDB protest, calling for Prime Minister Najib Abdul Razak to resign, in Kuala Lumpur, Malaysia November 19, 2016. REUTERS/Edgar Su TPX IMAGES OF THE DAY

Protesters clad in yellow shirts marched through the heart of Kuala Lumpur bringing traffic to a standstill in several tourist spots, wrapping up peacefully in front of the iconic Petronas Twin Towers after an initial plan to assemble at Independence Square was thwarted by police.

Najib has faced criticism since the Wall Street Journal reported last year that around $700 million (567 million pounds) from state fund 1Malaysia Development Berhad (1MDB) was diverted into the personal bank account of the prime minister.

Najib ran into further trouble when lawsuits filed by the U.S. Justice Department in July said over $3.5 billion was stolen from 1MDB, which was founded by Najib, and that some of those funds flowed into the accounts of “Malaysian Official 1”, whom U.S. and Malaysian officials have identified as Najib.

The demonstration is unlikely to shake the prime minister, who has denied wrongdoing and weathered the crisis, consolidating power by cracking down on dissenters.

Eleven activists and opposition leaders were arrested on Friday and at least two more were detained at the rally. The deputy Prime Minister Ahmad Zahid Hamidi said there could be more arrests in the coming days.

Maria Chin Abdullah, the chair of pro-democracy group Bersih that organised the rally, was detained under Malaysia’s Security Offences (Special Measures) Act, or Sosma, her lawyers said. The law was introduced in 2012 to protect the country from security and extremist threats.

Laurent Meillan, acting regional representative of the United Nations Human Rights Office in South-East Asia, said the use of Sosma was very concerning.

“Security legislation should not be used against peaceful demonstrators. We call for the immediate and unconditional release of Maria Chin Abdullah and other activists,” Meillan said.

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Another Bersih leader, Hishamuddin Rais, and artist Fahmi Reza were also arrested.

“We are not here to bring down the country. We love this country! We are not here to tear down the government, we’re here to strengthen it,” Bersih deputy chair Shahrul Aman Shaari told the crowds gathered at the National Mosque.

Najib has taken steps which critics say aim to limit discussion of the scandal, such as sacking a deputy prime minister, replacing the attorney-general, suspending newspapers and blocking websites.

Najib retains significant support within UMNO and from the long-ruling Barisan Nasional coalition.

‘ARREST US ALL’

Turnout was lower than a similar rally last year, with police saying that about 15,500 Bersih supporters took part, while news portal Malaysiakini estimated around 40,000. As many as 200,000 people showed up last year at one point.

Police had said the rally is illegal and that they would not hesitate to use tear gas or water cannon if things got out of hand. State news agency Bernama said about 7,000 policemen would be on duty near the protest areas.

Still, spirits were high among those that gathered, with drums heard along with speeches, songs and chants by participants calling for a clean Malaysia and people power.

Former Malaysian premier Mahathir Mohamad, Najib’s fiercest critic, joined protesters in front of the Twin Towers.

“Let him come and arrest us all. We will stand up for our leaders including Maria Chin who has been arrested for the wrong reasons,” said 91-year-old Mahathir.

Muhyiddin Yassin - the former deputy premier who was sacked and now leads a new party chaired by Mahathir - was also present, leading the crowds in chants of “Step down Najib!”

“Our country is being governed by clowns and crooks. So I’m here to protest against our prime minister,” said the artist Reza before being arrested.

Azalina Othman Said, a minister in the Prime Minister’s Department, on Saturday said it was unlawful for any party to try to unseat an elected government via street protests.

Fears of clashes between Bersih and a pro-Najib group called Red Shirts mounted earlier this week after the latter threatened to target Bersih supporters, though no major clashes were reported on Saturday.

The pro-Najib group also rallied on Saturday and police estimated that about 2,500 supporters of Najib turned up.

Jamal Yunos, an UMNO member and leader of the Red Shirts, was arrested on Friday. He had warned of a repeat of racial riots in 1969 that killed hundreds in clashes between Malays and ethnic Chinese.

Ethnic Chinese and Indian minorities formed the bulk of the Bersih rally, similar to last year.