KUALA LUMPUR, Malaysia — Police unleashed tear gas and chemical-laced water Saturday at thousands of demonstrators who staged one of Malaysia’s largest street rallies in years, demanding fair rules for national elections expected soon.

Malaysian police said in a statement that 222 people were arrested. Lawyers said most were expected to be released soon after having their details recorded, but it was not immediately clear if they would be charged later with any offense.

Officials said three demonstrators and 20 police were injured.

At least 25,000 demonstrators swamped Malaysia’s largest city, hoping to pressure Prime Minister Najib Razak’s ruling coalition — which has held power for nearly 55 years — to overhaul electoral policies before polls that could be held as early as June.

Authorities insist the elections will be free and fair, rejecting activists’ claims that the Election Commission is biased and that voter registration lists are tainted with fraudulent names.

Protesters waving banners and chanting slogans poured into downtown Kuala Lumpur, massing near a public square that police had sealed off with barbed wire and barricades.

“I’m here because I’m a Malaysian and I love my country,” said information technology manager Burrd Lim. “There’s no election that’s perfect, but I want one that’s fair enough.”

Authorities had refused to allow an opposition-backed pressure group that organized the rally to use Independence Square, a nationally renowned venue that hosts parades and patriotic celebrations.