"There was a pregnant woman among them. She lost blood and then she lost the baby," he said.



Some 3,000 mostly female workers were taking part in the demonstration when police in riot gear moved in.



The protest had blocked a road outside a factory owned by Sabrina (Cambodia) Garment Manufacturing in Kampong Speu province, west of the capital, Phnom Penh.



"Police used an electric baton to hit me on the head and if other workers hadn't pulled me away, I would be dead," Leng Pros, a 28-year-old male worker, said from his hospital bed. "I didn't know what happened next, I fell to the ground."



Police and military police officials declined to comment on the clash, saying they were still collecting reports.

Nike said in a statement: "We are concerned by the serious allegations related to one of our contract factories in Cambodia and are immediately investigating the latest reports.



"We have been in active discussions with this contract factory since last week and we continue to closely monitor the situation."



It added: "As outlined in Nike's Code of Conduct, Nike requires its contract manufacturers to respect their employees' rights to freedom of association."



The workers have been staging strikes and protests since May 21.



They want the company, which employs more than 5,000 people at the plant, to give them just over £9 ($14) each month to help pay for transport, rent and healthcare costs on top of their £49 ($74) minimum wage.



According to the International Monetary Fund, garments accounted for 75% of Cambodia's total exports of £3.45bn ($5.22bn) in 2011.