The Trump administration has imposed sanctions on Iran’s foreign minister, Mohammad Javad Zarif, striking at the main diplomatic channel between Iran and the west.

The US secretary of state, Mike Pompeo, said Zarif had been targeted because he acted on behalf of the supreme leader, Ali Khamenei.

“Foreign Minister Zarif is a key enabler of Ayatollah Khamenei’s policies throughout the region and around the world,” Pompeo said in a written statement. “The designation of Javad Zarif today reflects this reality.”

In a later tweet, Pompeo added: “He’s just as complicit in the regime’s outlaw behaviour as the rest of [Khamenei’s] mafia.”

Zarif responded quickly on Twitter, shrugging off the significance of the US move.

“The US’ reason for designating me is that I am Iran’s ‘primary spokesperson around the world’ Is the truth really that painful?” he asked. “It has no effect on me or my family, as I have no property or interests outside of Iran. Thank you for considering me such a huge threat to your agenda.”

Iran’s president, Hassan Rouhani, said the move was “childish” and a barrier to diplomacy.

Shortly after Washington announced the sanctions on Zarif, the White House’s national security advisor, John Bolton, said the US would renew sanctions waivers for Iranian nuclear programs that allow Russia, China and European countries to continue their civilian nuclear cooperation with Tehran.

“I think the idea here is we are watching those nuclear activities very, very closely,” Bolton said in an interview on Fox Business Network. “So this is a short 90-day extension,” he said.

A report in the Washington Post last week said the treasury secretary, Steven Mnuchin, had argued for renewing the waivers over the objections of Pompeo and Bolton because if they were not renewed, Washington would have to sanction Russian, Chinese and European firms involved in projects inside Iran as part of the 2015 nuclear deal.

The administration had first threatened to sanction Zarif last month, but relented to allow him to visit New York, while strictly limiting his freedom of movement within the city. During his stay in New York, the Iranian foreign minister is reported to have met Senator Rand Paul, who Donald Trump had said was seeking to help negotiations between the two countries.

Zarif was the chief Iranian negotiator in the 2015 deal, the Joint Comprehensive Plan of Action, from which the US withdrew in May last year. In the face of mounting US efforts to kill the agreement, the Iranian diplomat continued to meet his counterparts from Europe, Russia and China, who have been anxious to keep the deal afloat.

Tensions between the US and Iran escalated in May when Washington tightened sanctions, in effect barring all countries from buying Iranian oil.

Last month Iran seized of the British-linked oil tanker MT Riah in the strait of Hormuz, apparently in retaliation for the UK seizing the Iranian tanker Grace 1 off Gibraltar. Zarif accused London of “ doing the bidding for the Trump administration.”

“The Zarif designation is one of the most ridiculous steps I’ve seen this administration take. It won’t meaningfully affect Zarif’s diplomacy, it probably won’t result in much in terms of asset freeze or complications for him, and will annoy other world leaders,” said Richard Nephew, former principal deputy coordinator for sanctions policy at the state department.