LONDON, United Kingdom - Iran's Foreign Ministry has strongly criticized the United States for exerting pressure and resorting to threats after President Donald Trump warned of serious sanctions on countries buying Iranian oil.

In a statement on Friday, the ministry said the US sanctions were in breach of the UN Charter and international law. "Tehran will not tolerate any approach based on threats and pressure," the statement warned.

It condemned US pressure on Iran's trade partners, calling it another sign that justifies Iran's "deep mistrust" of American intentions.

In a post on his Truth Social account on Thursday, Trump warned that all purchases of Iranian oil or petrochemical products "must stop, NOW!" The US president asserted that any country or individual failing to comply "will be subject to, immediately, Secondary Sanctions," and "will not be allowed to do business with the United States of America in any way, shape, or form."

A day earlier, Iran announced that a pre-scheduled fourth round of nuclear talks with the United States—originally expected this weekend in Rome—had been postponed due to "logistical" issues. A new date has yet to be announced.

While reaffirming Tehran's commitment to diplomacy, the Foreign Ministry renewed earlier warnings in the Friday statement that sanctions could derail the already fragile diplomatic process aimed at resolving the nuclear standoff.

It noted that following Trump's letter to Iran's supreme leader in March, Tehran decided to enter the talks "in good faith and backed by national strength and trust." But the sanctions regime, the ministry said, is a failed strategy which would "only lead to the same costly failures of the past."

Tug of war over nuclear enrichment

In the first three rounds of talks, Tehran has been seeking sanctions relief in exchange for caps on its nuclear enrichment program. Tehran, however, insists that a full shutdown of its atomic facilities is non-negotiable.

But in a sign that the two sides had deep differences to bridge, US Secretary of State Marco Rubio argued on Thursday that the Islamic Republic must entirely abandon enrichment if it genuinely seeks a peaceful nuclear program.

In an interview with Fox News, Rubio stressed that Tehran must open all facilities to international, including American inspectors, cease support for "terror groups" and stop missile development.

"President Trump is a president of peace, but we cannot live in a world where Iran has a nuclear weapon," he concluded.