"The United States is prepared to use its domestic authorities to sanction any individual or entity that materially contributes to the supply, sale, or transfer of conventional arms to or from Iran," Pompeo said in a statement.

"Every nation that seeks peace and stability in the Middle East and supports the fight against terrorism should refrain from any arms transactions with Iran."

The embargo on the sale of conventional arms to Iran was due to begin expiring progressively from October 18 under terms of the UN resolution that confirmed the 2015 nuclear deal between Tehran and world powers.

Tehran, which could now purchase weapons from Russia, China and elsewhere, has hailed the expiration as a diplomatic victory over its archenemy the United States, which had tried to maintain an indefinite freeze on arms sales.

President Donald Trump withdrew the United States from the nuclear deal in 2018 and has unilaterally begun reimposing sanctions on Iran.

Pompeo said that "for the past 10 years, countries have refrained from selling weapons to Iran under various UN measures. Any country that now challenges this prohibition will be very clearly choosing to fuel conflict and tension over promoting peace and security."