File Photo: Somalia maritime police from PMPF patrol in the Gulf of Aden. AP
The tanker was seized northeast of the Somali city of Mareeyo on Tuesday, UKMTO said.
"Military Authorities have reported unauthorised persons taking control of the tanker and manoeuvring the vessel 77NM (nautical miles) south within Somali territorial waters," it said.
Somali authorities did not immediately respond to AFP queries about the hijacking.
On Thursday, UKMTO said a Somali-flagged fishing vessel had been hijacked by 11 "armed individuals", and an armed group separately boarded an oil-products tanker.
"Together, these events indicate a credible piracy threat," it said.
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