The United States said it was targeting five trading companies -- four based in the United Arab Emirates and one in Turkey -- that sold Iranian-origin petrochemical products to third countries, along with two firms involved in shipping.

"So long as Iran attempts to generate oil and petrochemical revenues to fund its destabilizing 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," Secretary of State Marco Rubio said in a statement.

The move comes just after Iran announced a fourth round of talks with President Donald Trump's administration to take place Saturday in Rome.

Iran is seeking sanctions relief as part of a deal on its contested nuclear program.

Trump's business friend and globe-trotting envoy Steve Witkoff has been leading the talks and voicing optimism for a deal, with Trump seeking to avoid an Israeli strike on Iranian nuclear sites.

In his first term, Trump tore up an earlier agreement with Iran negotiated by former president Barack Obama and Washington's European allies.

He imposed sweeping sanctions, including trying to ban Iran from selling oil to all other countries -- with China the key market.

The sanctions remain in place, although enforcement levels have varied.