TEHRAN: The US is acting alone against Tehran and its allies are too "ashamed" to join its forces in the Gulf, Iran's top diplomat said Monday, dismissing Washington's calls for talks as a sham.

Foreign Minister Mohammad Javad Zarif also confirmed he had turned down an offer to meet President Donald Trump last month despite the threat of US sanctions against him.

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

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

Tehran and Washington have been locked in a battle of nerves since last year when Trump withdrew the US from a landmark 2015 deal placing curbs on Iran's nuclear programme and began reimposing sanctions.

Tensions have soared since the Trump administration began stepping up a campaign of "maximum pressure" against Iran.

Drones have been downed and tankers seized by Iranian authorities or mysteriously attacked in Gulf waters, while Britain has detained an Iranian tanker off Gibraltar.

At the height of the crisis, Trump called off air strikes against Iran at the last minute in June after the Islamic republic's forces shot down a US drone.

Iran said on Sunday its forces had seized a "foreign" tanker carrying smuggled fuel in what would be the third such seizure in less than a month in Gulf waters -- a conduit for much of the world's crude oil.

- 'Arsonist cannot be fireman' -

Last month the Guards said they had impounded the Panama-flagged MT Riah for alleged fuel smuggling as well as the British-flagged Stena Impero for breaking "international maritime rules".

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

But it has been struggling to find partners, with European countries reticent and believed to be concerned about being dragged into a conflict.

The US plan suffered another blow on Monday when Germany said it was currently "not in favour" of joining an American-led coalition.

"The important thing is to continue to follow the path of diplomacy and to seek dialogue with Iran... to ensure the free movement of oil tankers in the Gulf," said government spokeswoman Ulrike Demmer.

Zarif blasted the idea of a US-led coalition.

"Why form a global coalition? America is responsible for tensions in the Persian Gulf, in the world," he said.

"An arsonist cannot be a fireman."

The veteran diplomat also slammed Britain over its July 4 seizure of a tanker carrying Iranian oil.

He accused London of "piracy" because the sanctions the vessel was accused of breaking -- on fuel deliveries to Syria -- only applied to EU members.

Zarif rejected claims the British-flagged Stena Impero had been seized in retaliation, saying that the vessel's case "must be investigated in Iranian courts".

Asked about reports he had been invited to meet Trump, 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 weeks unless I accepted that offer, which fortunately I did not," Iran's top diplomat said.

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 invited the Iranian minister to go to the White House.

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

- 'Trump doesn't seek war' -

The designation of Zarif under the same sanctions already applied to supreme leader Ayatollah Ali Khamenei is the latest in a series of US moves against Iran.

Zarif dismissed as disingenuous US "claims" it wants dialogue.

"They were the ones who left the table, sanctioned the foreign minister of Iran, sanctioned the highest authority of the Islamic republic. Who do they want to negotiate with?" he said.

But Zarif did not rule out talks in the future, saying: "Even in times of war negotiations will exist."

Zarif said he did not believe Trump would go to war with Iran unless hawks around him like his national security adviser John Bolton and Israeli Prime Minister Benjamin Netanyahu had their way.

"I believe Mr Trump does not seek war. But Mr Bolton and Netanyahu have always sought war," he said.

"They're willing to fight their wars till the last American soldier." —AFP