"The captain has passed away due to the injuries he sustained earlier," said Abdi Mohamoud Samatar, a pirate close to the gang which captured the MV Theresa VIII on Monday.

"He died of gunshot wounds," Samatar added.

It was not immediately clear whether the captain, whose nationality is as yet unknown, sustained injuries during Monday's hijacking or after the vessel was seized.

"He was taken to Harardhere to get medical attention and was again returned to the ship while he was in bad condition," Samatar explained, referring to a coastal village in northern Somalia.

The tanker was hijacked some 180 nautical miles northwest of the Indian Ocean archipelago.

It was headed to the Kenyan port of Mombasa, but the pirates turned it around and headed north, the European Union's anti-piracy mission in the region said on Tuesday.

The Virgin Islands-owned freighter is operated from Singapore.