Iranian President Hassan Rouhani accused the United States of "childish behavior" on Thursday over Washington's sanctioning of Iran's foreign minister amid rising tensions between the two countries.

The United States imposed sanctions on Iranian Foreign Minister Mohammad Javad Zarif on Wednesday, targeting the country's top spokesman and potentially hurting chances of diplomatic talks amid rising tensions between the two countries.

"They (Americans) are resorting to childish behavior... They were claiming every day 'We want to talk, with no preconditions'... and then they sanction the foreign minister," Rouhani said in remarks carried live on state television. "This means they have lost the power of rational thought."

Zarif, a critical figure in the 2015 Iran nuclear deal, dismissed the action and said it would not affect him.

China's stance

China firmly opposes the U.S. imposing unilateral sanctions or "long-arm jurisdictions," said Hua Chunying, spokesperson for the Chinese Foreign Ministry, during a regular press conference in Beijing on Thursday, reiterating China's position on the issue.

We hope that the words from the U.S. side would match their deeds as the country showed its willingness to hold talks with Iran recently, said Hua, adding that only dialogue can solve the problem.

The widening rift

U.S. President Donald Trump pulled the United States out of the deal last year and ramped up sanctions to put pressure on Iran's economy. The move dismantled part of President Barack Obama's legacy and upset U.S. allies who were party to the agreement, which was designed to restrict Tehran's pathway to a nuclear bomb in exchange for sanctions relief. 

Strains between Washington and Tehran have risen more in recent months after attacks on tankers in the Gulf that the United States blames on Iran and Iran's downing of a U.S. drone that prompted preparations for a U.S. retaliatory air strike that Trump called off at the last minute. 

"Javad Zarif implements the reckless agenda of Iran’s Supreme Leader, and is the regime’s primary spokesperson around the world. The United States is sending a clear message to the Iranian regime that its recent behavior is completely unacceptable," Treasury Secretary Steven Mnuchin said in a statement. 

The sanctions against Zarif would block any property or interests he has in the United States, but the Iranian foreign minister said he had none. 

"The U.S.' reason for designating me is that I am Iran's 'primary spokesperson around the world'," Zarif said on Twitter. "Is the truth really that painful? 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."

Zarif lived in the United States from the age of 17 as a student of international relations in San Francisco and Denver, and subsequently as a diplomat at the United Nations in New York, where he was Iranian ambassador from 2002 to 2007. 

The Trump administration said it would make decisions on whether to grant Zarif travel visas, including for trips to the United Nations, on a case by case basis, holding open the possibility that he might attend the annual UN General Assembly in September. 

If Zarif received such a visa, that would allow direct or indirect U.S. contacts with him during that gathering, which brings most of the world's leaders to New York and has been the venue for previous U.S.-Iranian contacts. 

A senior U.S. official reiterated that Trump was open to talks with Iran, but said the administration would want to deal with a key decision maker, which it did not consider Zarif to be.

Senator Chris Murphy, a Democratic member of the Senate's Foreign Relations Committee, questioned the administration's move. 

"If our position is really that we want to negotiate with Iran than maybe we shouldn’t sanction their chief negotiator," Murphy posted on Twitter. 

On June 24, Trump targeted Iranian Supreme Leader Ayatollah Ali Khamenei and other top Iranian officials with sanctions.

Mnuchin said then that Zarif would be blacklisted that week, but the designation did not happen quickly. Reuters reported in mid-July that the administration had decided to hold off on sanctions against him for the time being. 

The Trump administration still sought a diplomatic solution, U.S. Secretary of State Mike Pompeo said on Wednesday. But Zarif's foreign ministry was advancing the Iranian Supreme Leader's "destabilizing" policies, he added.

"The only path forward is a comprehensive deal that addresses the full range of its threats. Until then, our campaign of diplomatic isolation and maximum economic pressure will continue," said Pompeo. 

Mnuchin claimed that Zarif used social media to spread Iranian "propaganda and disinformation" while the government did not allow its citizens to use such mediums themselves.

(With input from Reuters)