Incoming US army chief says Washington is trying to put together a coalition to provide escort to commercial shipping.

The Pentagon says it is discussing military escorts for vessels in the Gulf, a day after Iranian ships allegedly tried to block a United Kingdom oil tanker near the strategic Strait of Hormuz.

The White House’s nominee to become chairman of the Joint Chiefs of Staff, General Mark Milley, said on Thursday Washington was attempting to put together a coalition “in terms of providing military escort, naval escort to commercial shipping”.

“I think that that will be developing over the next couple weeks,” Milley told the Senate Armed Services Committee.

Earlier, the US Fifth Fleet said it was working closely with the British Royal Navy as well as regional and global partners to defend freedom of navigation through the region.

“The United States Fifth Fleet is aware of the Islamic Revolutionary Guard Corps Navy’s unlawful harassment and attempts to interfere with the passage of the UK-flagged merchant vessel British Heritage on 10 July, near the Strait of Hormuz,” Vice Admiral Jim Malloy, Commander US Fifth Fleet, said in a statement.

A spokesman for the US military’s Central Command said threats to navigation required an international solution.

On Tuesday, Marine General Joseph Dunford, the outgoing chairman of the joint chiefs of staff, said the US was working to enlist allies in a military coalition to safeguard strategic waters off Iran and Yemen.

A British Royal Navy patrol vessel guards the oil supertanker Grace 1, that’s suspected of carrying Iranian crude oil to SyriA [Jon Nazca/Reuters]

UK ships on high alert

A British security source said London had already raised its threat warning level for British ships in Iranian waters to the highest possible category earlier this week.

Three Iranian vessels tried to impede the oil tanker passing through the strait, but backed off when confronted by a Royal Navy warship, Britain said on Thursday.

“We are concerned by this action and continue to urge the Iranian authorities to de-escalate the situation in the region,” the UK said in a statement.

Iran’s elite Revolutionary Guard (ICRG) denied blocking the British tanker which came a week after Britain seized an Iranian tanker off Gibraltar believed to be headed to Syria in violations of European Union sanctions.

Iranian officials have since been quoted as suggesting Tehran might retaliate against British shipping.

Earlier, Iran‘s Foreign Minister Mohammad Javad Zarif dismissed as “worthless” the allegation that Tehran sought to block the ship.

The US blames Iran for a series of attacks on shipping in the world’s most important oil artery since mid-May, accusations Tehran rejects.

The foes came as close as ever to direct military conflict last month, when Iran shot down a US surveillance drone and Trump ordered retaliatory air attacks, only to call them off minutes before impact.

Iran ship captain arrested

Meanwhile, police in the British territory of Gibraltar said on Thursday they had arrested the captain and chief officer of the Grace 1 supertanker accused of violating EU sanctions on Syria and seized documents and electronic devices from the ship.

A senior Iranian military commander on Thursday said Britain and the US would regret detaining the vessel.

Al Jazeera’s Zein Basravi, reporting from Tehran, said that the arrest of senior officers of the Grace 1 tanker will escalate the tensions even further.

“Many senior Iranian leaders say the UK action was taken at the behest of the US,” Basravi said.

“Iranians are angry that the tanker with 2 million barrels of crude oil was seized, something Iran will find it difficult as it’s trying to sell its oil in the face of the unilateral US sanctions.”

Tensions have risen since the Trump administration quit an agreement last year between Iran and world powers to curb Tehran’s nuclear programme and slapped new sanctions.

Washington sharply tightened sanctions against Iran since May with the aim of bringing its oil exports to zero. Iran responded by stepping up production of enriched uranium beyond limits in the nuclear deal.

Trump has said he won’t allow Iran to develop nuclear weapons but Tehran says its nuclear activity is within the framework of the 2015 nuclear deal.

The European nations, who are also signatory to the deal, have disagreed with Trump’s decision to quit the landmark agreement but urged Tehran not to exceed nuclear enrichment limit.

The US sanctions have effectively driven the Islamic Republic from mainstream oil markets, depriving it of its main source of revenue and of the benefits it was meant to receive from its nuclear deal.

Iran says it will return to full compliance with the agreement only if sanctions are lifted and Washington rejoins the pact.