The meeting in Tehran between Abbas Araghchi and Helga Schmid, deputy to EU foreign policy chief Federica Mogherini, focused on the 2015 nuclear deal while also touching upon "regional and international issues", according to IRNA news agency.

The talks follow attacks Thursday on two tankers in the Gulf of Oman that the United States has blamed on Iran, despite Tehran's denials.

US-Iran strains have escalated since President Donald Trump withdrew last year from the landmark nuclear deal which Iran signed with world powers.

The European Union is an ardent backer of the deal and has pledged to support Tehran in the face of crippling US sanctions, but Iranian officials have voiced frustration at the lack of concrete steps taken so far.

Tehran has given the remaining partners of the deal until July to make good on their pledges, or warned it will step back from its key nuclear commitments.

Schmid's stop in Tehran follows visits last week by German Foreign Minister Heiko Maas and Japanese Prime Minister Shinzo Abe.

The latter was in the Iranian capital when the tanker attacks happened, with explosions hitting a Japanese-owned vessel and a Norwegian-operated one.

The incident near the Strait of Hormuz, a key waterway which is vital to the world's oil supply, has raised fears of conflict erupting in the region.