The US has announced new sanctions against Iran over its nuclear programme, a day after the two countries held the fourth round of talks in Oman.

The latest sanctions target three Iranian nationals and an entity with links to Iran's Organisation of Defensive Innovation and Research, also known by its Persian acronym SPND. “All individuals sanctioned are involved in activities that materially contribute to, or pose a risk of materially contributing to, the proliferation of weapons of mass destruction,” Secretary of State Marco Rubio said in a statement on Monday.

“Iran continues to substantially expand its nuclear programme and carry out dual-use research and development activities applicable to nuclear weapons and nuclear weapons delivery systems,” he added.

Mr Rubio said Iran was the only country in the world without nuclear weapons that is producing uranium enriched to 60 per cent. Building a weapon requires 90 per cent but the amount hugely exceeds the 3.67 per cent maximum that was imposed by the 2015 nuclear deal that US President Donald Trump left during his first term.

Iran insists its nuclear programme is for peaceful and civilian purposes only.

The latest sanctions came a day after the fourth round of talks between Washington and Tehran – mediated by Muscat – aimed at entering a new nuclear deal and preventing Iran from acquiring a nuclear weapon.

Iran described the latest negotiations as “difficult but useful” and that a new date for the next round would be announced later. A senior US official described Sunday's talks positively, confirming that another round would take place soon.

Iranian Foreign Minister Abbas Araghchi has also been liaising with regional countries on the talks with the US. In a phone call with his Egyptian counterpart Badr Abdelatty, the two discussed the latest round of talks, according to Iranian state media.

Mr Araghchi was also in Saudi Arabia, Qatar and the United Arab Emirates days before Mr Trump began his regional tour. The US president was set to arrive in Riyadh on Tuesday, kicking off his first official visit.

In Abu Dhabi, Mr Araghchi discussed the talks with his Emirati counterpart, “emphasising the importance of these discussions in bolstering regional security and stability and preserving international peace and security,” Wam reported.