(Recasts with Nigerian comment, previous BEIJING)

By Ani Akpan

CALABAR, Nigeria, May 10 (Reuters) - Three Chinese construction workers abducted in a remote southeast Nigerian state were released unharmed on Friday, government officials said on Saturday.

The three employees of China Civil Engineering Construction Corp (CCECC) were abducted on Thursday by their local driver who was suspected to have collaborated with other Nigerian staff of the company, to press for improved wages and working conditions.

The abduction was not related to the kidnappings for ransom that are common in the oil-producing Niger Delta where militants have launched a campaign of violence to press for local control of the region's natural resources.

A spokesman for the government of Cross River state, where the Chinese workers, one of them CCECC's finance manager, were kidnapped, said the trio reappeared at the company's site at Ikono in neighbouring Akwa Ibom state.

"We don't really know how they were released, we were just surprised to see them at the company's gate in Ikono around 7-8 p.m. (1800-1900 GMT). They were unhurt and no ransom was paid," Patrick Ugbe told Reuters.

Ugbe said the government has launched an investigation to get at the root of the incident. He added the whereabouts of the Nigerian driver was still unknown.

China's foreign ministry said in a statement on its website the three men were safe, but did not give further details.

They were returning to the firm's residential compound from a construction site near the state capital Calabar, when their driver diverted the car to an unknown destination.

Ugbe had told reporters on Friday that Nigerian employees of CCEC had given a protest letter to Cross River state Governor Liyel Imoke on Tuesday, when he visited a site where the company is building a bridge, complaining about poor wages and welfare.

There are widespread complaints in Africa's top oil producer that Asian companies pay low salaries and treat local workers like slaves. The firms deny the allegations. (Additional reporting by Ken Wills; writing by Tume Ahemba; editing by Alex Richardson and Matthew Jones) (For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/)

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