SEOUL (Reuters) - Two Vietnamese crewmen on a South Korean fishing vessel in the Indian Ocean have allegedly stabbed and killed the ship's captain and the engineer over a dispute, South Korea's coast guard said Monday.

The two, both aged 32, have since been overpowered by other crew members and are locked up aboard the vessel as it sails to the Seychelles capital Victoria, a coast guard official in South Korea's southern city of Busan said.

The attack against the captain and the engineer took place early morning South Korean time Monday and was reported to the coast guard by the vessel's owner located in Busan, coast guard official Kim In-ho said by telephone.

The Vietnamese crew members were believed to be drunk at the time of the incident, Kim said. "They are said to have been unhappy with the orders given by Korean bosses," he said, adding their exact motive will have to be investigated.

South Korean maritime police will dispatch a team of investigators to the island state on Tuesday, and the suspects will be brought back to South Korea, Kim said.

(Reporting by Jeong-eun Lee; Editing by Jack Kim and Michael Perry)