In co-ordination with international and regional forces operating in the area, the United States is increasing the rotation of ships and aircraft patrolling in and around the Strait of Hormuz after Iran's recent, unlawful seizures of merchant vessels.
The US Navy's 5th Fleet, which is based in Bahrain, said in a statement that it was working with allies and partners to protect the crucial chokepoint into the Gulf.
"We've seen repeated Iranian threats, arm seizures and attacks against commercial shippers who are exercising their navigational rights and freedoms in international waters and strategic waterways of the region," US National Security Council spokesman John Kirby told reporters on May 12.
"The United States will not allow foreign or regional powers to jeopardise freedom of navigation through the Middle East waterways including the Strait of Hormuz," he said.
Commanders at US Naval Forces Central Command (NAVCENT) and French Forces Deployed in the Indian Ocean (ALINDIEN) discussed the new rotations and tactics on May 13.
Iran seizes two ships in one week
Two oil tankers recently seized by Iran are anchored off the coast of one of its key port cities on the Strait of Hormuz, The Associated Press (AP) reported on May 7.
Satellite photos from Planet Labs PBC showed the Advantage Sweet and the Niovi anchored near a naval base just south of Bandar Abbas in Iran's Hormozgan province on May 6.
Iran's Navy seized the Marshall Islands-flagged Advantage Sweet on April 27 as it traveled in the Gulf of Oman, carrying Kuwaiti crude oil.
The reason for the seizure was unclear, but a US official told Al-Monitor that Iran's move could be related to the case of the Suez Rajan, another Marshall Islands-flagged tanker reportedly under US investigation.
The Suez Rajan is under US Department of Justice investigation for allegedly ferrying sanctioned Iranian oil in the South China Sea, the media outlet said.
Satellite images showed a second ship, the Niovi, a Panama-flagged tanker, which was seized by Iran's Islamic Revolutionary Guard Corps (IRGC) in the Strait of Hormuz on May 3.
The tanker was sailing from Dubai towards the Emirati port of Fujairah when it was stopped by the IRGC's Navy (IRGCN), the US Navy said.
"The IRGCN subsequently forced the oil tanker to reverse course and head toward Iranian territorial waters off the coast of Bandar Abbas," it said.
While it was not carrying any cargo, data from S&P Global Market Intelligence seen by the AP showed the Niovi in July 2020 received oil from a ship known then as the Oman Pride.
The Liberian-flagged crude oil tanker Oman Pride was sanctioned by the US Treasury in August 2021 for being "involved in an international oil smuggling network" that has been helping Iran circumvent sanctions on oil exports.
"Iran's continued harassment of vessels and interference with navigational rights in regional waters are a threat to maritime security and the global economy," the US Navy said in an April 27 statement.
Long history of harassment
The latest seizures are just the latest in a long history of Iran harassing, attacking and interfering with internationally flagged merchant vessels.
In many such instances, Iran seizes vessels and their crews so they can be turned into pawns in negotiations with the West.
Several recent examples are indicative of these manipulative tactics.
In November, Iran released two Greek oil tankers that it had seized in the Gulf in May, ending a months-long diplomatic impasse that had strained relations between Athens and Tehran.
The Prudent Warrior and Delta Poseidon were each carrying about one million barrels of oil when they were seized shortly after Tehran warned it would take "punitive action" against Athens over the confiscation of Iranian oil by the United States from a tanker held off the Greek coast.
In January 2021, the Iranian navy seized the South Korean tanker Hankuk Chemi as it transited the Strait of Hormuz. The tanker was seized as Iran sought the release of Iranian funds frozen in South Korean banks.
The ship was released four months later.
In August 2021, suspected Iran-backed forces attempted to hijack the MV Asphalt Princess tanker, boarding the vessel and ordering it to sail to Iran. The suspects left the vessel when US and Omani ships arrived.
Later that year, IRGC naval forces took control of Vietnamese-flagged oil tanker M/V Sothys in the Gulf of Oman, emptied its cargo of crude oil in Bandar Abbas before releasing it back at sea two weeks later, according to USNI News.
After the incident, Tanker Trackers -- an international tanker tracking website -- published a track of Sothys from June 2021 in which the tanker took on 700,000 barrels of cargo from M/V Oman Pride.
The tanker attempted to offload the oil in China in August, the tracking website said, but was turned away and sent back to Iran due to sanctions.
It concluded that Sothys went back to Iran to shed the oil for another attempt at a sale.
In July 2020, the oil tanker Gulf Sky disappeared from waters off the United Arab Emirates (UAE), along with its Indian crew.
The following month, it turned up in Iran where it was later suspected of working as a "ghost ship" -- helping the regime ferry oil in breach of sanctions, according to the BBC.
Records show Gulf Sky's transponder was switched off for weeks after the alleged hijacking. In late August 2020, when it was first turned on, the vessel was floating off the coast of southern Iran.
Gulf Sky has since been renamed Rima and has also changed hands and is now owned by a Tehran-based mining company, Moshtagh Tejarat Sanat (MTS), the BBC said.
MTS's managing director Amir Dianat, a longtime associate of senior officials of the IRGC's Quds Force (IRGC-QF), was sanctioned by the US Treasury in May 2020 for helping the IRGC-QF generate revenue and smuggle weapons abroad.
In July 2019, the IRGC seized British-flagged tanker Stena Impero with its 23 crew members aboard in the Strait of Hormuz.
The oil tanker was held in the Iranian port of Bandar Abbas for two months and only released after international pressure.
In April 2015, Iran seized the Maersk Tigris as it was also sailing in the Strait of Hormuz, over a legal dispute that Iran said had no political implications.
Despite those claims, the method in which the IRGC Navy (IRGCN) captured the ship, surrounding it in an international shipping lane and firing across its bow, raised many eyebrows, USNI News reported.
The merchant ship was released over a week later.