He is one of 24 crew members on the Maersk Tigris, which was in international waters crossing the Strait of Hormuz en route from Jeddah in Saudi Arabia to Jebel Ali in the UAE when it was approached and seized by Iranian patrol boats.
A spokesman for Denmark-based Maersk said they understand the “crew is safe and under the circumstances in good spirits”.
A statement added: “We are continuing our efforts to obtain more information about the Iranian authorities’ seizure - in international waters - of Maersk Tigris. We are not able at this point to establish or confirm the reason behind the seizure.
“We remain in close dialogue with the Danish Ministry of Foreign Affairs.”
A Pentagon official said Iranian forces fired warning shots across the bridge of the cargo vessel, boarded the ship and directed it towards the Iranian mainland.
The ship is managed and crewed by Rickmers Ship Management, based in Hamburg, Germany, which said communication with the ship had been established in the last few hours.
A spokesman for Rickmers said the ship is very close to the Iranian coast and confirmed that a British man was on board.
He said the ship is carrying “general cargo” and the other crew members are mainly eastern European and Asian.
The incident with the Maersk Tigris, which prompted the US Navy to dispatch a destroyer and a plane, comes at a critical time in Iran’s relations with its neighbours and the US.
Iranian state television reported that the ship was seized based on a court order due to unspecified violations.
The Strait of Hormuz is the route for about a fifth of the world’s oil and is only about 21 miles wide at its narrowest point.
Iran has in the past threatened to block the strait, a move that could spark military conflict in the Gulf.
US and allied naval forces routinely patrol the strait and have conducted military drills aimed at countering threats such as sea mines that Iran might use to close the waterway.