The European Union's disagreement with the United States over Iran widened when the EU vowed on Thursday to continue working with Iranian Foreign Minister Mohammad Javad Zarif despite the latest US sanctions against him.

The US Treasury Department announced on Wednesday its sanctions on Zarif. "Javad Zarif implements the reckless agenda of Iran's Supreme Leader, and is the regime's primary spokesperson around the world," US Treasury Secretary Steven Mnuchin said in a statement. The US put sanctions on Iranian Supreme Leader Ayatollah Ali Khamenei on June 24.

"We regret this decision," said Carlos Martin Ruiz De Gordejuela, a spokesman for EU foreign policy chief Federica Mogherini.

"From our side, we will continue to work with Mr Zarif as Iran's most senior diplomat and in view of the importance of maintaining diplomatic channels," he said, as quoted by the Agence France-Presse.

The EU has been trying to salvage the 2015 Iran nuclear deal, officially known as the Joint Comprehensive Plan of Action (JCPOA) that was reached in July 2015 by Iran and China, France, Germany, Russia, the United Kingdom and the US. US President Donald Trump pulled the US out of the deal last May and reimposed sanctions on Iran, endangering the implementation of the agreement also endorsed by the UN Security Council.

The EU has created a special purpose vehicle, known as Instex, to facilitate financial transactions for European companies doing trade with Iran. The recent appointment of former German ambassador to Iran Bernd Erbel to head Instex was aimed at expanding the mechanisms, according to the Bourse& Bazaar.

Zarif, 59, has been Iran's foreign minister since 2013 and led Iran's successful negotiations in the JCPOA. With his US educational background and rich experience in international organizations, the career diplomat and academic is known for his wisdom and a good sense of humor and as an effective communicator.

"The US' reason for designating me is that I am Iran's 'primary spokesperson around the world'. Is the truth really that painful?" Zarif said on social media on Thursday.

"It has no effect on me or my family, as I have no property or interests outside of Iran. Thank you for considering me such a huge threat to your agenda."

The US move on Wednesday has been seen as contradicting Trump's claim to open new talks with Iran. US Secretary of State Mike Pompeo, a key hawkish figure in the maximum pressure campaign against Iran, has urged the Iranian government to let him visit the country.

But he was quickly mocked by Zarif. "Instead of making empty and disingenuous offers, @Sec-Pompeo can accept any of the many requests from Iranian reporters to interview US officials," Zarif said in a tweet on Thursday. "He has refused til now, as he knows he has to be accountable to rigorous questioning - the very same way I am by the US media."