A senior U.S. official says Iranian naval ships and patrol craft fired shots at a cargo ship in the Strait of Hormuz before escorting it into Iranian territorial waters.

The official said the container ship, the MV Maersk Tigris, was tansiting the strait into the Arabian Gulf “on an internationally recognized maritime route” at the time of the incident. 

Pentagon spokesman Col. Steve Warren says the container ship was in Iranian waters when it was approached.

“The ship master was contacted and directed to proceed further into Iranian territorial waters,” Warren said. “He declined and one of the IRGCN craft fired shots across the bridge of the Maersk Tigris. The master complied with the Iranian demand and proceeded into Iranian waters in the vicinity of Larak Island.”

Pentagon officials say a U.S. guided missile destroyer, the USS Farragut, is en route to the area.  U.S. Naval Forces Central Command has also  “directed aircraft to observe the interaction between the Maersk vessel and the IRGCN [Iranian] craft.”

U.S. officials have been in touch with representatives of the shipping company, who say Iranian forces have boarded the vessel.

A senior administration official says the container ship did issue a distress call but that the call came after shots had been fired.

The MV Maersk Tigris is a Marshall Island-flagged vessel. U.S. officials say no Americans were on board.

According to Iran’s Farsnews agency, “The Iranian Navy has confiscated the American trade vessel with all its 34 crew for trespassing on Iran’s territorial waters in the Persian Gulf.”

Iran has in the past sometimes threatened to block the strait to advance its opposition to sanctions imposed over its nuclear program.

The channel is a narrow strip of water separating Oman and Iran. It connects the biggest Gulf oil producers, such as Saudi Arabia, with the Gulf of Oman and the Arabian Sea.

At its narrowest point, the strait is 33 km (21 miles) across and consists of 2-mile wide navigable channels for inbound and outbound shipping and a 2-mile-wide buffer zone.