The United States said on Wednesday it was imposing sanctions on seven companies involved in selling Iranian oil -- four based in the United Arab Emirates and one in Turkey.

US Secretary of State Marco Rubio said: "So long as Iran attempts to generate oil and petrochemical revenues to fund its destabilising activities, and support its terrorist activities and proxies, the United States will take steps to hold both Iran and all its partners engaged in sanctions evasion accountable."

The move came ahead of a fourth round of Iran-US talks on Saturday in Rome, where Tehran is seeking relief from sanctions in return for curbs on its nuclear programme.

In a statement, Iran's foreign ministry spokesman Esmaeil Baqaei said the sanctions were part of US efforts "to disrupt friendly and legal relations between developing countries through economic terrorism".

He said they were "clear evidence of the contradictory approach of American decision-makers and their lack of goodwill and seriousness in advancing the path of diplomacy".

Since returning to office in January, US President Donald Trump has reinstated a campaign of "maximum pressure" on Iran, mirroring his approach during his first term, while also calling for dialogue.

In March, he sent a letter to Iran's supreme leader Ayatollah Ali Khamenei, who has the final say in major state policies, urging talks and warning of possible military action if Iran refused.

During his first term, Trump withdrew the United States from the 2015 nuclear deal between Iran and world powers and reimposed biting sanctions, prompting the Islamic republic to roll back its commitments.