SOCHI, Russia (AFP) - The International Olympic Committee (IOC) said on Wednesday it is taking "firm" action with the Russian authorities to ensure all the workers who built the Sochi 2014 facilities are paid in full.

The failure of the companies contracted to build the sports and hotel facilities to pay thousands of workers millions of dollars in salaries on time has cast a shadow over Russia's hosting of the Games.

IOC spokesman Mark Adams insisted the Olympics body had already pressured the Russian authorities on the issue.

He said 500 companies had already been investigated and it turned out that US$8 million (S$10.1 million) of wages had not been paid to workers.

Funds have now been paid to 6,175 workers, he told reporters.

Adams acknowledged that some workers still had not been paid, although he did not give figures. "I would almost certainly agree that probably not every single person has been paid," he said.

"The IOC is taking some really firm action, working with Sochi 2014, to try and ensure this happens," he added. "I think we can show quite a lot of action, quite a lot of will to get this done."

Thousands of migrant workers, largely from the poorest ex-Soviet Central Asian states of Tajikistan, Kyrgyzstan and Uzbekistan, were involved in the frenetic push to build the Sochi infrastructure on time.

Human Rights Watch has said hundreds of workers told local activists they had not been paid and has described the exploitation of migrants as casting a "shadow on the Sochi Games' glittering facade".

Transfers from migrants working in Russia back home make a crucial contribution to the economies of Central Asian states and are estimated to make up half of the GDP of Tajikistan.