(Updates with Japanese official, paragraphs 4-5)

By David Chance

KUALA LUMPUR, Aug 21 (Reuters) - Pirates hijacked two more vessels, an Iranian bulk carrier and a Japanese-operated tanker, on Thursday off the coast of Somalia in some of the world's most dangerous waters, the International Maritime Bureau said.

That came after a Malaysian tanker carrying 39 crew and a cargo of palm oil was hijacked in the same area on Wednesday.

"Both ships were attacked and hijacked this morning," said Noel Chong, head of the International Maritime Bureau piracy reporting centre in Kuala Lumpur. The Japanese tanker had 19 crew on board, but no Japanese nationals, he said.

An official at Japan's Transport Ministry said that vessel was a Panama-registered chemical tanker.

He said its operating company was not Japanese, but that it subcontracted some management responsibility to a Japanese firm. The official did not name either company.

Piracy is rife off Somalia, which has been mired in anarchy since warlords overthrew a dictator in 1991. Last week, Somali pirates hijacked two other ships -- a Thai cargo ship, the MV Thor Star, and a Nigerian tug boat, the MT Yenegoa Ocean.

Local gunmen are also holding a Japanese-managed bulk vessel, the MV Stella Maris, that was hijacked on July 20.

Abdikadir Musa Yusuf, assistant fisheries minister in northern Somalia's semi-autonomous Puntland region, said local officials had been in touch with the crew of the Malaysian oil tanker when it was seized in the Gulf of Aden on Wednesday.

"Our radar crews could hear them screaming for help but we had no power to fight the pirates," he told Reuters. "We hear the tanker is now heading towards Eyl, the pirates' base." (Additional reporting by Abdiqani Hassan in Bosasso and Osamu Tsukimori in Tokyo; Editing by Daniel Wallis and MacDonald Dzirutwe)

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