The US is unable to build a naval coalition to escort tankers in the Gulf because its allies are too "ashamed" to join it, Iran's foreign minister said Monday.

"Today the United States in alone in the world and cannot create a coalition. Countries that are its friends are too ashamed of being in a coalition with them," Foreign Minister Mohammad Javad Zarif told a news conference in Tehran.

"They brought this situation upon themselves, with lawbreaking, by creating tensions and crises."

Iran and the US have been locked in a battle of nerves since May 2018 when President Donald Trump withdrew the US from a landmark 2015 deal placing limits on Iran's nuclear program and began reimposing sanctions.

Tensions soared after the Trump administration stepped up a US campaign of "maximum pressure" against Iran, with drones downed and tankers mysteriously attacked in Gulf waters.

In response, the US has been seeking to form a coalition whose mission - dubbed Operation Sentinel - it says is to guarantee freedom of navigation in the strategic Gulf waters.

However, it has been struggling to build such a coalition, with European countries reticent and believed to be concerned about being dragged into a possible conflict.

Asked on Monday about reports that he had been invited to meet Trump in the White House, Zarif said he had turned it down despite the threat of sanctions against him.

"I was told in New York I would be sanctioned in two week[s] unless I accepted that offer, which fortunately I did not," said the Iranian minister.

The New Yorker magazine reported on Friday that Senator Rand Paul met Zarif in the US on July 15 and had Trump's blessing when he extended an invitation to the Iranian minister to go to the White House.

The US imposed sanctions against Zarif on Wednesday, targeting any assets he has in America and squeezing his ability to function as a globe-trotting diplomat.