SEOUL (REUTERS) - Three Chinese fishermen were killed on Thursday (Sept 29) in a fire that broke out on their boat when South Korean coastguard men trying to apprehend them for illegal fishing threw flash grenades into a room they were hiding in, a South Korean official said.

The three men were believed to have suffocated, a coastguard official in the South Korean port city of Mokpo said, adding that the incident was being investigated.

Disputes over illegal fishing are an irritant in relations between China and US ally South Korea, even as their economic relations grow close. They also share concern about North Korea's nuclear weapon and missile programmes.

The fire broke out in the boat's steering room, said the official, who is not authorised to speak with media and declined to be identified, told Reuters by telephone.

A Chinese embassy official in Seoul could not be reached for comment and China's foreign ministry in Beijing did not immediately respond to a request for comment.

South Korean authorities were questioning the 14 surviving crew and coastguard members involved in the operation, the official added.

South Korean coastguard vessels regularly chase Chinese boats for fishing illegally and violent confrontations have occurred in the past.

The Chinese boat, caught fishing in waters off the south-west of the peninsula, about 70 km south-west of Hongdo Island, would be brought in to a South Korean port later on Friday, the official said.

In June, South Korea and the United Nations Command, which overseas the Korean War armistice, launched a joint operation to keep Chinese fishing vessels from operating illegally off South Korea's west coast.

That came after South Korean fishermen, frustrated with incursions by Chinese boats in defiance of coastguard warnings, impounded two Chinese trawlers and handed them over to authorities.