DUBAI -- Iran's seizure last week of a US-bound Marshall Islands-flagged tanker in the Gulf of Oman follows a familiar pattern, with the UN Navy slamming Iran's "continued harassment of vessels".
The tanker had been transiting international waters in the Gulf of Oman when, according to Iran, it collided with an Iranian vessel.
"The Iranian government should immediately release the oil tanker," the US Navy's Bahrain-based 5th Fleet said in a statement, saying it was monitoring the situation.
"Iran's actions are contrary to international law and disruptive to regional security and stability," it added.
"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 latest flare-up is one of a spate of such incidents in recent years, and comes just days after Tehran's Western rivals toughened sanctions on the Islamic Revolutionary Guard Corps (IRGC).
The 5th Fleet initially blamed the IRGC for the seizure of the vessel but then said the capture was carried out by Iran's navy.
It identified the vessel as the oil tanker Advantage Sweet and said the tanker had issued a distress call during the seizure.
Iran's navy said the "violator" ship was captured after a collision with an Iranian ship that left two crew members missing and several injured.
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.
Aggression in regional waters
The sensitive waters of the Gulf are a chokepoint for at least a third of the world's seaborne oil.
Thursday's seizure is just the latest incident in and around the Strait of Hormuz where ships have been mysteriously attacked, drones downed and oil tankers seized.
Regional experts have accused the IRGC of interfering with the communications and navigation systems of commercial vessels in the Strait of Hormuz and Gulf waters.
This is a political game intended to confuse ships so they will inadvertently stray into Iranian waters, where IRGC forces will seize them, they told Al-Mashareq.
In response to increased Iranian hostility, the United States has bolstered its airpower in the region, sending for the first time on March 31 a US Air Force A-10 Thunderbolt II attack aircraft to al-Dhafra air base in the United Arab Emirates (UAE).
The A-10 -- the first aircraft designed specifically for close air support -- can destroy adversary forces and infrastructure, including tanks and attack ships.
Analysts say the A-10s would be particularly devastating against fast attack boats, such as the ones used by the IRGC near the Strait of Hormuz.
"In the past two years, Iran has unlawfully seized at least five commercial vessels sailing in the Middle East," the US Navy said.
The MarineTraffic tracking website last showed the Advantage Sweet, owned by Advantage Tankers, off the coast of Oman. The crude oil vessel had departed from Kuwait and was en route to the US city of Houston, it said.
On Friday, Advantage Tankers said in a statement sent to AFP that the tanker "is currently being escorted by the Iranian Navy to a port on the basis of an international dispute".
In July 2019, the IRGC seized the British-flagged oil tanker Stena Impero in the same waterway for allegedly ramming a fishing boat, and released it two months later.
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.
On July 29, 2021, a drone attack on the MT Mercer Street off the port of Fujairah killed the ship's Romanian captain and a British security guard. The US military concluded that Iran was behind the attack.
On August 4, 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.
In May 2022, Iran seized two Greek oil tankers.
'Shots fired' at vessel off Yemen
In a separate incident in the volatile area on Friday, shots were fired at a vessel in waters south of Yemen, a British navy organisation said.
An unidentified vessel in the Gulf of Aden came under attack, said United Kingdom Maritime Trade Operations (UKMTO), which provides security alerts for the shipping trade.
Three boats were involved in the attack with three to four people onboard each, the brief statement said. No further details were given.
The UKMTO is involved in anti-piracy operations and is part of Britain's Royal Navy, which co-ordinates surveillance in the region.
Previous attacks have been blamed on Somali pirates, but they have fallen in recent years as a result of international security operations.
In January 2022, Yemen's Iran-backed Houthis seized an Emirati-flagged vessel in the Red Sea.
On Monday, the United States, Britain and the European Union toughened sanctions against the IRGC, citing alleged human rights violations.
The Western measures add to ones already taken over Tehran's hardline response to protests that rocked Iran since the September death of 22-year-old Mahsa Amini in the custody of the "morality police".
Amini had been arrested for an alleged breach of strict dress rules for women.
US sanctions also targeted the new Secretary of Iran's Supreme Council of Cyberspace, the authority responsible for Iran's cyberspace policy and blockage of popular websites.
"The Iranian people deserve freedom of expression without the threat of violent retaliation and censorship from those in power," said Treasury official Brian E. Nelson.
"Along with our key allies and partners, such as the United Kingdom, the United States will continue to take action against those responsible for the regime's violent repression and censorship."