At least four Cambodian workers were killed on Friday, and more than 39 others were wounded, when police in Phnom Penh opened fire on a crowd of protesters demanding higher wages.

In addition, at least 23 people have been arrested; their whereabouts remain unknown.

Human rights organisations describe the incident as the worst state violence against civilians in more than a decade.

According to witnesses on the ground, AK-47 rifles were used by armed forces to quell the demonstration.

In an interview with the French news agency AFP, a military police spokesman, Kheng Tito, justified the crackdown, saying nine policemen had been injured by violent protesters. He also said if the strikes were to continue, the situation would turn into “anarchy”.

On Thursday, a day before the bloodshed, police also arrested several high-ranking union figures. Amongst them is Vorn Pao, president of the Independent Democracy of Informal Economy Association (IDEA), and Theng Savoeum, coordinator of the Coalition of Cambodian Farmer Communities (CCFC).

Both organisations are members of the Cambodian Labour Confederation (CLC) and the Cambodian Coalition of Apparel Workers Democratic Union (CCAWDU).

These incidents have sparked outcry from international trade unions.

In a letter addressed to Prime Minister Hun Sen, the general secretary of the International Trade Union Confederation (ITUC) Sharan Burrow wrote: “I write in horror as we witness the continued violence perpetrated by members of the police and armed forces against striking garment workers.

“For police to kill, beat and arrest workers in brazen violation of the fundamental right to freedom of association is extremely troubling and must be condemned.”

Her statement was echoed by Jyrki Raina, general secretary of IndustriALL: “The right to strike for a higher minimum wage is solidly protected by the international right to freedom of association, enshrined in ILO Convention 87 – which Cambodia ratified in 1999.

“The threats, arrests, and the killing of trade unionists for the exercise of that right is an extremely grave violation and must be condemned. Any encouragement of that violence by garment manufacturers must end.”

A massive uprising against Hun Sen

This violent crackdown comes amid growing dissent against the country’s strong man Hun Sen, who has been in power for nearly 30 years.

His contested election in July 2013, which many independent monitors say was rigged, culminated in massive rallies at the end of December when tens of thousands of protesters marched through the streets of the capital city of Phnom Penh to demand that he step down.

Planned talks with the opposition Cambodia National Rescue Party, led by Sam Rainsy, were cancelled as a result of the latest violence, and the government banned all public gatherings.

The Cambodian labour movement has been at the forefront of the struggle, which gained further momentum on 24 December, 2013 when garment workers went on strike to protest against a minimum wage proposal in the textile industry that fails to meet decent living wage.

The movement quickly spread to some 800 footwear and textile factories, forcing many of them to shut down, after an initial offer to increase the minimum monthly salary from US$80 to US$95 per month (later US$100) was rejected by two unions that are pushing for US$160, which is double the current wage.

But employers reject this level of pay, saying it would make the industry uncompetitive.

The Garment Manufacturers’ Association of Cambodia (GMAC) even threatened to move production if labour unrest was not quashed and praised the government for its lethal use of force against the protesters.

The garment industry in Cambodia employs more than half a million workers.

It is a key source of national income, supplying brands such as Gap, Nike and H&M, and bringing about US$5 billion in export revenue to one of Asia’s poorest countries.