US Navy warships stationed in the Persian Gulf have increased their patrols through the Strait of Hormuz, the busy merchant shipping passage, in response to Iran’s latest move to seize two oil tankers, the latest sign of rising tensions between Iran and the United States.

“Iran’s actions are unacceptable,” said Vice Adm. Brad Cooper, the commander of US naval forces in the region, in an interview Monday at the Navy base here in Bahrain. He spoke several days after riding one Navy guided missile destroyer through the Strait of Hormuz, along with leaders from the French and British navies, in an attempt to send a unified message to Iran.

Iran has “harassed, attacked or interfered” with 15 internationally flagged merchant ships since 2021, Pentagon and White House officials said this month, as they announced the move to increase patrols by US Navy ships, drones and aircraft, as well as United’s. states’ allies in the region.

Most recently, Iran’s navy flew a helicopter over the deck of an oil tanker with the name Advantage Sweet at the end of April. The Marshall Islands-flagged ship had been chartered by Chevron, bound for Houston from Kuwait, and according to Lloyd’s List, which tracks shipping, it was transports 750,000 barrels of crude oil.

Commandos from Iran’s Islamic Revolutionary Guard Corps descended to Advantage Sweet’s deck via a rope and took control of the ship just after it had passed through the Strait of Hormuz. Iran then showed one festive video of the seizure on state television.

Six days later, a dozen motorboats from the Iranian Navy surrounded a second oil tanker, this time the Panama-flagged Niovi, after it left a dry dock in Dubai, bound for another port in the United Arab Emirates. The ship was forced to divert to Iranian territorial waters.

The United States “will not allow foreign or regional powers to jeopardize freedom of navigation in the Middle East waterways, including the Strait of Hormuz,” said John Kirby, a spokesman for the White House National Security Council, in announcing the increased U.S. fleet. patrols earlier this month.

The Strait of Hormuz, which borders the United Arab Emirates and Oman on one side and Iran on the other, is as narrow as 21 miles. But it sees constant merchant ship traffic, especially among oil tankers that deliver oil to the world.

The plan, at least for now, is not to send additional Navy ships or aircraft to the region, Pentagon officials said, but instead to move those already in the area through the Strait of Hormuz more often, to send a signal to Iran that the United States and its allies are watching on, and to be in closer proximity if other incidents take place, said Cmdr. Timothy Hawkins, spokesman for the Navy’s Fifth Fleet based in Bahrain.

The Navy’s Fifth Fleet operations cover 2.5 million square kilometers of water, from the Persian Gulf to parts of the Indian Ocean, and more of its ships will now be focused on the area around Iran.

“It’s kind of like when you rotate more patrol cars on a highway,” Commander Hawkins said. “They go off the exit and turn back and keep doing these loops.”

On Tuesday, a US Coast Guard cutter, preceded by a drone ship that the Navy operates in the Persian Gulf, sailed through the Strait of Hormuzalong with the guided-missile destroyer USS Paul Hamilton, which had also made the same trip on Friday.

In response to the latest US actions, Iran has argued that its action against the two merchant ships came after they both violated international maritime rules, including the Advantage Sweet, which Iranian officials claim had collided with an Iranian boat, injuring crew members.

“The Islamic Republic of Iran considers the continued presence of foreign military forces in the waters of the Persian Gulf as a threat to the security of navigation in this strategic waterway and believes that the countries of the region have the ability to protect the peace and security of navigation in it without the presence of foreigners,” said Nasser Kanani, spokesman for Iran’s Ministry of Foreign Affairs, said in a statement.

In April, just before Iran seized the oil tanker Advantage Sweet bound for Houston, the United States stopped a ship carrying Iranian oil that the government says violated sanctions, according to Ambrey, a naval intelligence firm, which first reported by the Financial Times. US authorities said the seizure had been authorized under a court order.

Dating back to at least the mid-1980s – when there was a period nicknamed the Tanker War due to a series of attacks by Iran on merchant ships in the Strait of Hormuz – there have been cycles of escalation in the region as ship eavesdropping by Iran has intensified or subsided.

There is always a risk that the sparring between the US and Iran could quickly turn into a conflict, but both countries want to avoid such an outcome, say experts on the region, as well as US Navy officials.

“It’s almost like Kabuki theater that both countries have engaged in for a very long time, even though the reality of a serious armed conflict is almost unthinkable for both nations,” said John Ghazvinian, director of the Middle East Center at the University of Pennsylvania and the author of a book about history relations between Iran and the United States.

But animosity between the two nations has increased in recent years. Two ship crew members were killed in July 2021 when an Iranian-built drone armed with explosives attacked the merchant vessel Mercer Street, off Oman, an incident that US and European officials said thought Iran was behind it.

The US had already used its navy and coast guard ships in the region to search for weapons and drugs being shipped through the Persian Gulf, as Iran has been accused of helping arm its allies in Yemen, Syria and Lebanon, and more recently, of sending its attack drones to Russia, where they have been used to attack Ukraine.

Tensions have also intensified since the Trump administration’s 2018 withdrawal of the United States from a nuclear deal with Iran, which has since moved again to begin enriching its uranium supply closer to the levels needed to produce a nuclear weapon.

The Pentagon announced in April that it is extending the tour of the aircraft carrier George HW Bush in the eastern Mediterranean and accelerating the deployment of Air Force A-10 attack aircraft to a base in the Middle East. It did too rare public announcement that the US sent a guided missile submarine to the Middle East.

Mr Ghazvinian said the Pentagon’s latest action could be an attempt to reaffirm US relevance in the region, after China stepped in in March to help negotiate a diplomatic rapprochement between Saudi Arabia and Iran. Some Gulf Arab officials said China’s growing presence suggested they could no longer rely on the United States to guarantee their security.

Commander Hawkins, the Navy spokesman, said both the United States and Iran had the right to patrol the Persian Gulf and the Strait of Hormuz and had done so for decades.

Erik Schmitt contributed reporting from Washington.