LAGOS: Nigerian police said on Tuesday they had freed three Chinese workers kidnapped last week from a gold-mining site in southwestern Osun state.

The Chinese were abducted and their police escort killed on February 1 following a dispute with local labourers at the mining site at the Atakumosa area of the state.

"We have rescued the three Chinese expatriates. They were freed on Sunday," state police spokeswoman Yemisi Opalola told AFP.

She said the foreigners became ill while in captivity and were being given medical care.

She said that no arrests had been made.

It was not immediately clear if a ransom was paid for their release and police did not provide further details on how they had been rescued.

Kidnapping for ransom used to be common in Nigeria's oil-producing south but has lately spread to the other parts of the country.

The victims are usually released after a ransom is paid although police rarely confirm if money changes hands.

Chinese firms are working in Nigeria on multi-billion-dollar infrastructure projects that include mining, railways, airports and roads.

Their workers have been repeatedly targeted by kidnap gangs.

Last July, four Chinese workers were abducted from a quarry site in southern Cross River state while their police guard was killed.

They were released one month later.