Iran's foreign minister Tuesday condemned the imposition of US sanctions on neighbouring Turkey over its procurement of Russia's S-400 air defence system, saying it showed "contempt for international law".

"We strongly condemn recent US sanctions against Turkey and stand with its people and government," Mohammad Javad Zarif tweeted, using the hashtag "#NeighborsFirst".

On Monday, Washington banned all US export licences and loan credits for Ankara's military procurement agency, and said it would not allow its president to travel or hold assets in the United States.

Secretary of State Mike Pompeo said the sanctions would send "a clear signal" that the US "will not tolerate significant transactions with Russia's defence and intelligence sectors."

But Zarif, whose country has been under crippling US sanctions since 2018 when the administration of outgoing President Donald Trump abandoned a nuclear agreement between it and major powers, said the move against Ankara showed how quickly Washington resorted to sanctions.

"US addiction to sanctions and contempt for international law at full display again," he said.

Turkey took delivery of the S-400 air defence system from Russia last year despite US warnings it was incompatible with its membership of the NATO alliance.

President Recep Tayyip Erdogan said imposing sanctions would be "disrespectful" and Turkey pressed on with testing the new system.

Zarif's defence of Turkey comes days after he sharply criticised Erdogan for reciting a poem seen as supporting the union of Iran's mainly Azeri-speaking northwestern provinces with neighbouring Azerbaijan.

But on Monday, President Hassan Rouhani moved to draw a line under the row, saying he found it "unlikely" that Erdogan wanted to "insult the nation of Iran or our territorial integrity".

"We can put this issue behind us with the explanations they have given," Rouhani said.