Cambodia’s opposition leaders have been summoned to court on suspicion of inciting civil unrest, as Premier Hun Sen moves to quash growing unrest.

Cambodia National Rescue Party leader Sam Rainsy and his deputy, Kem Sokha, have been summoned to Phnom Penh Municipal Court on January 14 for questioning, according to warrants posted on the opposition website late on Saturday.

The opposition party has boycotted parliament since the July elections, alleging widespread vote rigging.

Hun Sen faces an increasing challenge to his nearly three-decade rule from striking garment workers and opposition supporters demanding he step down and call a new election because of alleged vote fraud.

On Friday, police opened fire on striking garment factory employees demanding a minimum wage of $160 a month for their work in an industry that supplies brands such as Gap, Nike and H&M.

Rights activists said at least four civilians were shot dead in what they described as the country’s worst state violence against its citizens in 15 years.

A day later, dozens of security personnel armed with shields and batons chased hundreds of protesters – including monks, women and children – from their rally base in a park in the capital, according to activists.

Police and civilian thugs “used metre-long steel poles to beat and intimidate the peaceful protesters” before tearing down the rally site, according to the Cambodian League for the Promotion and Defence of Human Rights.

Police have indefinitely banned further rallies, including one that had been planned for Sunday.

Freedom Park, also known as Democracy Park, was opened by the government in 2010 as a designated area for people to air their grievances, and protesters had occupied the site since December last year as part of demonstrations against the contested election.

An estimated 20,000 or more opposition supporters took to the streets of the capital a week ago to demand Hun Sen step down.

Cambodia’s leader has faced mounting criticism over his rights record as well as accusations of excessive force used against demonstrators.

Rainsy, his main opponent, returned from self-exile in July after a royal pardon for convictions he denounced as politically motivated, but he was barred from running in the election the same month.