WASHINGTON: The United States on Thursday imposed sanctions on companies it accused of playing a critical role in the production, sale and shipment of Iranian petrochemicals and petroleum to buyers in Asia, as Washington increases pressure on Tehran.

The US Treasury Department in a statement said it imposed sanctions on six Iran-based petrochemical manufacturers and their subsidiaries and three firms in Malaysia and Singapore over the production, sale and shipment of hundreds of millions of dollars worth of Iranian petrochemicals and petroleum.

“Iran increasingly turning to buyers in East Asia to sell its petrochemical and petroleum products, in violation of US sanctions” Treasury’s Under Secretary for Terrorism and Financial Intelligence, Brian Nelson, said in the statement.

“The United States remains focused on targeting Tehran’s sources of illicit revenue, and will continue to enforce its sanctions against those who wittingly facilitate this trade.”

The latest US move against Iranian oil smuggling comes as efforts to revive Iran’s 2015 nuclear deal have stalled and ties between the Islamic Republic and the West are increasingly strained as Iranians keep up anti-government protests.

OnTuesdaythe head of the United Nations nuclear watchdog underscored the urgency of resuscitating diplomatic efforts to limit Iran’s nuclear programme, saying the situation could quickly worsen if negotiations fail.

Rafael Mariano Grossi, director general of the International Atomic Energy Agency, said the diplomatic effort “is not at its best point,” but it wasn’t his place to declare whether the process was “dead or alive.’’ However, he said progress is not impossible.

“I hope to be able to re-set, restore, reinforce that indispensable dialogue,” he said during a discussion at the Chatham House think tank. “Without that, things are going to get worse.’’

Iran began rebuilding its nuclear stockpile after former U.S. President Donald Trump abandoned a 2015 agreement that limited the Islamic Republic’s atomic energy program. Talks on restoring the deal ended in August when western countries presented the “final text” of a roadmap for progress, which Iran has yet to accept.

Grossi warned last month that Iran had enough highly enriched uranium to build “several” nuclear weapons if it chose to do so. But diplomatic efforts aimed at once again limiting the country’s atomic program seem more unlikely than ever as Tehran provides arms for Russia’s war in Ukraine and as unrest shakes the Islamic Republic.

Grossi said the Middle East has a “unique set of problems” that will be aggravated if diplomatic efforts fail.

“I don’t see it in anybody’s interest that there will be proliferation there. I think we would be aggravating … the already fragile situation,’’ he said. “We’re not there yet. But we cannot really afford to fail.’’