If the Americans have "true intentions, let them release some of our assets, for example $10 billion frozen in foreign banks", Hossein Amir-Abdollahian said in an interview with state television broadcast late Saturday.

"But the Americans are not prepared to unlock them for us to be assured that they've taken into account the interests of the Iranian people at least this one time over the past decades," he said.

Amir-Abdollahian also warned that Tehran would sue South Korea if it continued to refuse to honour a debt of almost $8 billion for purchases of Iranian oil.

Iran's funds are frozen in South Korean banks.

"US pressure (on Seoul) is a fact but we cannot continue... to turn a blind eye to this question," he said, adding the government would allow the central bank to take legal action against two South Korean banks holding the funds.

Amir-Abdollahian said he had addressed the issue on Thursday during a telephone conversation with his South Korean counterpart Chung Eui-yong and asked him to allow Iran access to its assets "as soon as possible".

US Secretary of State Antony Blinken on Thursday renewed warnings that time was running out for Iran to return to the 2015 nuclear deal between Tehran and world powers.

"The ball remains in their court, but not for long," Blinken told reporters. "There is a limited runway on that, and the runway is getting shorter."

Former president Donald Trump withdrew from the deal and reimposed sweeping sanctions -- under which foreign banks have also frozen Iranian funds -- that Tehran wants removed before it reverses a series of steps it took to protest the pressure campaign.

The Biden administration had been engaged in indirect talks in Vienna with Iran on returning to compliance.

Iran requested a break in talks in June due to a political transition as the ultraconservative Ebrahim Raisi took over as president.

The parties to the 2015 deal with Iran saw it as the best way to stop the Islamic republic from building a nuclear bomb -- a goal Tehran has always denied.