Iranian forces have boarded a Maersk-owned vessel, says Pentagon spokesman Steve Warren according to Reuters.
The forces have allegedly also opened fire on the vessel.
The ship MV Maersk Tigris is currently on charter with Rickmers Shanghai, who is thus responsible for the vessel, Maersk tells Danish news media DR Nyheder.
Iranian patrol vessels fired warning shots and ordered the ship to sail further into Iranian waters when the ship was passing through the Strait of Hormuz.
At first, Maersk Tigris ignored the order, but then the vessel obeyed the order after the warning shots were fired.
US security forces in the region responded to distress signals from the cargo ship, and destroyer USS Faragut has been dispatched to the region to monitor the situation along with surveillance planes, adds Warren.
Maersk Tigris reportedly ran into trouble when the Iranian authorities deemed that the vessel was violating territorial borders. The ship was transiting the Strait of Hormuz.
The vessel, which sails under the Marshall Islands flag, is not carrying any Americans on board, says the Pentagon spokesman, thus rejecting information from Arabian news network al-Arabiya which stated that the ship was carrying 34 US seafarers on board.
Various news agencies report difficulties getting information from the Iranian authorities. According to Reuters, Iran has in the past threatened to block the strait in retaliation against international sanctions.