The ship Sibu 1 sent out a distress signal when it was about 136 nautical miles, just over 250 miles, east of the Yemeni port city of al-Mukalla, according to the shipping monitor Vanguard.
"The tanker is reported to have been boarded by six armed individuals, who are now in control of the vessel and are diverting it towards Somalia," the EU's Maritime Security Centre in the Indian Ocean (MSCIO) said.
A similar incident occurred earlier this week, when a cargo ship was hijacked off Marraye, Somalia.
Pirates were active off the coast of Somalia from around 2000 until 2011. After that, pirate activity declined, thanks in part to international efforts. However, pirate attacks have been reported again this year.
