The 19-metre Nigerian-flagged Utai 8 was heading for Port Harcourt when contact was lost 30 miles south of Brass on Wednesday morning.
It was carrying three crew.
The attack took place in the same area as a failed raid on Euronav's 150,000-dwt suezmax Cap Theodora (built 2008) earlier in April, and the scene of a hijacking on board L&B's 1,740-teu boxship Hansa Marburg (built 2007) on Monday, during which four crew were seized by gunmen.
