Iran President Hassan Rouhani on Thursday said the United States’ sanctions against his Foreign Minister Javad Zarif show that America is “afraid” of the top diplomat, AFP reported.

The United States had on Wednesday imposed sanctions on Zarif because he acted on behalf of the country’s Supreme Leader Ayatollah Ali Khamenei. The US had placed sanctions on Khamenei himself on June 24. Under these sanctions, Zarif’s properties and interests in the US will be blocked.

“Iran’s Foreign Ministry is not merely the diplomatic arm of the Islamic Republic but also a means of advancing many of the Supreme Leader’s destabilizing policies,” US Secretary of State Mike Pompeo said in a statement. Zarif and his ministry take their direction from Khamenei and are key enablers of the supreme leader’s policies throughout the region, he said.

Zarif, however, seemed unconcerned about the sanctions and posted a sarcastic tweet on Thursday saying it will have “no effect” on him. “The US’ reason for designating me is that I am Iran’s ‘primary spokesperson around the world’,” Zarif wrote. “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.”

“This action represents another step toward denying the Iranian regime the resources to enable terror and oppress the Iranian people,” Pompeo’s statement added. “Instead of using Iran’s precious resources to invest in the brave and rightfully proud people of Iran, the Iranian regime facilitates and supports terrorism, jails and tortures innocent Iranians, fuels foreign conflicts in Syria and Yemen, and, in recent weeks, has expanded its nuclear program.”

Describing Zarif as a senior official and an apologist for the regime, Pompeo said he was complicit in these “malign activities”. “The United States continues to seek a diplomatic solution that addresses the Iranian regime’s destructive behaviour,” Pompeo said. “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.”

Tensions between Iran and the United States have steadily increased since June, when Tehran shot down an American spy drone over the Strait of Hormuz. While Iran claimed the drone had violated its airspace, the US maintained it was shot down over international waters. The incident came days after the United States accused Iran of attacking two of its oil tankers in the Gulf of Oman on June 13.

In July, Iranian intelligence ministry officials said they had arrested 17 local spies associated with the United States’ Central Intelligence Agency and sentenced some of them to death. US President Donald Trump, however, dismissed these claims as “totally false”.

Tensions between Iran and other countries have also escalated recently. Last month, Iran captured a British tanker in the Strait of Hormuz after the United Kingdom’s Royal Marines seized an Iranian tanker near Gibraltar on July 4. As many as 18 Indians, including the captain, were on board the British tanker that Iran’s Islamic Revolutionary Guard Corps had seized, claiming it was in violation of international maritime regulations.