A fourth round of Iran-US talks over Tehran's nuclear programme has been postponed.

The foreign minister of Oman, facilitating negotiations, said Saturday's talks in Rome were being rescheduled because of logistical reasons, adding that a new date would be set when agreed by all sides.

It comes after US Secretary of Defense Pete Hegseth on Thursday warned that Iran would "pay the consequence" for its support of Yemen's Houthi rebels. Washington has also announced sanctions this week on companies it says have links to Tehran.

President Donald Trump pulled the US out of a previous nuclear agreement between Iran and five other world powers in 2018, and has long said he would make a "better" deal.

Trump has previously warned of military action if these new talks, which began in April, do not succeed. Both sides described the first round of talks in Oman's capital Muscat as "constructive".

Iran's foreign ministry confirmed that latest stage of talks had been postponed, but Washington is yet to officially comment.

However, an unnamed US source told the Reuters news agency that Washington "never confirmed" its participation in the fourth round of talks, nor had their timing been confirmed.

The delay is unlikely to mean that the talks have broken down, with both sides eager to avoid war.

But reports from Tehran have described growing doubt about the usefulness of the talks, pointing to the new sanctions and what Tehran calls contradictory positions from the US delegation.

Part of Trump's "maximum pressure" policy toward Tehran, the sanctions announced on Wednesday target entities said by the US to be involved in the illicit trade of Iranian petroleum and petrochemicals.

The US State Department said in a statement: "The Iranian regime continues to fuel conflict in the Middle East, advance its nuclear program, and support its terrorist partners and proxies.

"Today, the United States is taking action to stem the flow of revenue that the regime uses to fund these destabilizing activities."

Iran's foreign ministry spokesperson said the latest sanctions were "further proof of the American decision-makers' contradictory behaviour and lack of good faith".

Media reports in Iran also pointed to Hegseth's post on X earlier on Thursday, which was reposted by Trump's Special Envoy to the Middle East Steve Witkoff who has been leading the US delegation.

"Message to IRAN: We see your LETHAL support to the Houthis. We know exactly what you are doing. You will pay the CONSEQUENCE at the time and place of our choosing," the post read.

The Houthis have declared themselves part of an "axis of resistance" of Iran-affiliated groups against Israel, the US and the wider West -along with armed groups such as Hamas and Lebanon's Hezbollah movement.

The US has launched several deadly strikes on Houthi targets in recent months in response to the group's attacks on shipping in the Red Sea, which began in November 2023 in response to Israel's military campaign in Gaza.

Trump has said that he is looking for a solution that would close Iran's pathways to build a nuclear bomb. But there are those in his administration who are pushing for the complete dismantlement of Iran's nuclear enrichment programme.

They are also pushing for Iran to stop support for its proxies in the region, including the Houthis.

Iran says its programme is peaceful and that it has a right to enrichment. It is hoping for a deal to limit, but not dismantle, its nuclear programme in exchange for sanctions relief.

After Russia, Iran has been under the most extensive set of sanctions in history – the sanctions that the US has imposed on the country.

President Massoud Pezeshkian has centred Iran's economic policies on the promise of the lifting these sanctions.