Iranian naval commando (file)
Iranian naval commando (file) Reuters

After refusing to condemn the Iranian act of opening fire on and seizing a Marshall Islands ship in international waters last Tuesday, US State Department spokesperson Jeff Rathke revealed on Monday that the US is trying to free the ship "diplomatically."

"We have made a variety (of efforts) to help secure the release of the ship," said Rathke in a press conference. He said the seizure is not "consistent with the international law of the sea," but did not elaborate any consequences against Iran.

Iranian naval ships demanded the Maersk Tigris cargo ship enter Iranian waters to be seized as it was sailing in an internationally recognized shipping lane in the Strait of Hormuz.

The ship, which is said to be largely owned by American investors even though no Americans were on board, submitted after the Iranian ships fired warning shots across its bow. It is currently being held docked by the Larak Islands off Iran's coast, reports The Hill.

International treaties obligate the US to react to any attack on the Marshall Islands as if it was against America.

"We're in discussion with the Republic of the Marshall Islands on the basis of our compact with them to determine steps and the way forward," Rathke said Monday.

He said the US has "a defense responsibility which also includes shipping," but that the US is for now only involved in "diplomatic communications" with the Marshall Islands and the shipping companies.

"We remain in contact with them to peacefully resolve the incident and ensure safe passage for the vessel and its crew," he said.

Rathke refused to answer when asked if the US has directly talked to Iran about the ship.

Despite the negotiations over its nuclear program that are being coalesced into a deal ahead of a June 30 deadline, Iran has been showing a highly aggressive posture towards the US on the seas.

Just four days before the Maersk Tigris was captured, Iranian naval vessels encircled a US-flagged cargo ship in the Strait of Hormuz.

The US has increased its defense of US-flagged ships in the Strait since the incidents, with the US Navy starting to accompany American ships through the Strait last week.

On Monday the US announced it will accompany British-flagged ships as well, with Rathke noting, "there are discussions ongoing with other nations to include their vessels as well."