The captain of the Maersk Tigris cargo ship seized by Iranian authorities is a Bulgarian citizen, the Foreign Ministry in Sofia said on Wednesday.

Bulgaria’s ambassador in Tehran has sought a meeting with Iranian authorities over the seizure of the ship as well as detailed information about the state of the Bulgarian citizen, according to the Foreign Ministry.

The 65,000-tonne vessel bearing the flag of Marshall Islands was sailing through the Strait of Hormuz in international waters when Iranian Navy patrol boats ordered it to stop and escorted it to the port of Bandar Abbas on Tuesday, Maersk Line, the Danish shipping company that had chartered it, said in a statement, according to Reuters.

Maersk Line spokesman Michael Storgaard said in a statement that Iranian authorities told the company the ship's seizure related to an allegedly unresolved cargo claim, according to the AP.

"We are in ongoing contact with Rickmers Ship Management and are pleased to learn that the crew (are) safe and under the circumstances in good spirits," Maersk said.

The ship is being managed by Singapore-based Rickmers Ship Management company.

Citing Iranian state television reports, the AP said that the crew members were from Britain, Bulgaria, Romania and Myanmar.

Six Romanian citizens are on board the Maersk Tigris, according to Romanian media reports.