The United States said Monday it was imposing sanctions on Iran's defense ministry and Venezuelan President Nicolas Maduro under a UN authority which is widely contested.

"For nearly two years corrupt officials in Tehran have worked with the illegitimate regime in Venezuela to flout the UN arms embargo," Secretary of State Mike Pompeo told reporters.

"Our actions today are a warning that should be heard worldwide."

Pompeo said that President Donald Trump has issued an executive order "that is a new and powerful tool to enforce the UN arms embargo."

Treasury Secretary Steven Mnuchin, appearing with Pompeo, also announced separate sanctions on the Atomic Energy Organization of Iran.

The Trump administration argues that it is enforcing a UN arms embargo that Iran has violated, including through an attack on Saudi oil facilities.

But it is using a UN resolution that blessed a 2015 nuclear accord with Iran negotiated by former president Barack Obama.

Trump pulled out of the resolution with fanfare in 2018 but argues that the United States is still a "participant" in the accord as it was listed in the 2015 resolution.

The legal argument has been rejected by virtually all nations on the UN Security Council, including US allies.