The continued detention of one of its tankers in Iran is "unacceptable and unjustifiable", Stena Bulk said in a statement Tuesday.

The Swedish shipowner said crewmembers aboard the 50,000-dwt Stena Impero (built 2018) are fine as its arrest stretches into a third week, but the crew wonders how long they will have to stay in the Islamic republic.

"We are maintaining limited communication with the crew aboard and although they remain in good health considering the circumstances, we continue to be concerned about their welfare given the amount of...