The move is in response to ‘Iranian threats, armed seizures and attacks’ on shipping vessels, US official says.

During a news briefing on Friday, John Kirby accused Iran of harassing, attacking or interfering with the navigational rights of 15 internationally-flagged commercial vessels over the past two years.

“Today, the Department of Defense will be making a series of moves to bolster our defensive posture in the Arabian Gulf,” the White House spokesman told reporters.

It remains unclear what additional assets the US military will move to the region.

“We have seen repeated Iranian threats, armed seizures and attacks against commercial shippers who are exercising their navigational rights and freedoms in international waterways,” Kirby added.

Iran seized two international oil tankers in the Strait of Hormuz, including one headed to the US, in late April and early May.

Iranian officials said one of the tankers collided with an Iranian vessel and tried to flee, while the other was taken into Iranian territorial waters as the result of a judicial order following a legal complaint.

But the Reuters news agency reported that the seizures followed the confiscation of an Iranian oil tanker by the US days earlier that had not been publicly announced.

US authorities have tried to seize Iranian oil ships in international waters in the past to enforce unilateral sanctions on Iran’s nuclear programme, often sparking retaliation from the Iranian authorities in the Gulf.

The US Navy’s Fifth Fleet said on Wednesday that it was pushing to deter threats and “working with regional allies and partners to increase the rotation of ships and aircraft patrolling in and around the Strait of Hormuz following Iran’s recent unlawful merchant vessel seizures”.

It accused Iran of violating international law. “Iran’s unwarranted, irresponsible and unlawful seizure and harassment of merchant vessels must stop,” Vice Admiral Brad Cooper, who heads the Bahrain-based US fleet, said in a statement.

The recent spike in Iran-US tensions comes amid stalled diplomacy between the two countries.

The administration of US President Joe Biden has continued to impose and enforce a strict sanctions regime against Iran and its oil and petrochemicals industries.

This week also marked five years since former President Donald Trump uniliterally withdrew from a multilateral nuclear deal that saw Iran scale back its nuclear programme in exchange for a lifting of international sanctions against its economy.

Biden, who was vice president when the 2015 agreement was signed, had promised to revive the pact, but numerous rounds of indirect talks over the past two years have failed to restore it.

While Washington often reiterates that it will never allow Tehran to build a nuclear weapon, US officials have recently said they are no longer focused on the nuclear talks as they address other issues related to Iran, which has denied seeking nuclear arms.

US-Iranian relations have been further complicated by a crackdown on anti-government protests in Iran and Washington’s allegations that Tehran supplied Russia with drones that Moscow used against Ukraine.

Meanwhile, Iran signed a Chinese-brokered pact with Saudi Arabia in March to re-establish diplomatic relations with the Gulf kingdom. US officials have vaguely welcomed the agreement, saying it could lead to curbing Iran’s “destabilising actions”.