Cambodian police have fired warning shots at a brief clash with striking garment workers demanding higher wages, a state official and a local rights group have said.

Thousands of Cambodian factory workers, led by opposition leader Sam Rainsy, have been demonstrating in the capital of Phnom Penh for weeks now, calling for a higher minimum wage and for resignation of Hun Sen, the prime minister.

The violence broke out when military police tried to move the workers off a road on the outskirts of the capital Phnom Penh, according to Am Sam Ath of Licadho, a local rights group.

The workers then threw rocks at the authorities who fired "many warning shots" into the air and hit protesters with their batons, he told AFP news agency. Several people on both sides were reportedly injured.

With tens of thousands of garment workers on strike on Friday across the country, activists voiced fears of further violence.

"There are a lot of workers and if authorities use force against them, the violence would spread," Am Sam Ath said, urging unionists and authorities to hold talks to settle the problem.

'We had to prevent them'

The security forces said they were forced to act after workers damaged factory property.

"Because they used violence, we had to prevent them," military police spokesman Kheng Tito told AFP.

"If we did not fire warning shots into the air, they would have totally destroyed the economic zone."

Rong Chhun, president of the Cambodian Confederation of Unions, blamed authorities for the latest clash.

"We strongly condemn the authorities for the violence against workers who are demanding an appropriate wage," he said.

Disputes over wages and safety conditions are common in Cambodia's huge garment industry which supplies famous brands like Gap, Nike and H&M.

The government announced earlier this week that the monthly minimum wage for garment workers would be increased from $80 to $95 starting from April next year. The workers are demanding a minimum wage of $160 per month in 2014.

The sector employs about 650,000 people and is a key source of foreign income for the impoverished country.

Source: Agencies