Iran’s foreign minister said Monday that recent U.S. sanctions against him marked a “failure” for diplomacy and suggested that the measures were taken after he declined an invitation to meet President Trump at the White House. 

Imposing financial restrictions on a foreign minister means “failure in negotiations, failure in diplomacy and an opposition to dialogue,” Mohammad Javad Zarif said Monday at a news conference in Tehran, which was carried live by Iranian state television. 

The Treasury Department’s Office of Foreign Assets Control sanctioned Zarif last week for acting “for or on behalf of” Iran’s supreme leader, Ayatollah Ali Khamenei, who was also recently placed under U.S. sanctions. Zarif has said that the restrictions will have little practical effect, as he has “no property or interests outside of Iran.”

He said Monday that an invitation from Trump to visit the White House was extended last month when he traveled to New York for meetings at the United Nations.

U.S. officials have not confirmed the account, but the New Yorker magazine reported last week that Sen. Rand Paul (R-Ky.), whom Trump said he had authorized to speak with Zarif, relayed the message in a meeting with the foreign minister.

“I’m not going to make remarks on what happened in the negotiations, but I was told in New York that I would be sanctioned in two weeks unless I accepted that offer, which fortunately I did not,” Zarif said. 

“We are standing tall,” he continued. “The enemies cannot stop Iran’s progress with sanctions and pressure.” 

His remarks come amid a rise in tensions between Iran and the United States, which withdrew last year from a 2015 nuclear deal that Tehran struck with world powers. The Trump administration has since embarked on a “maximum pressure campaign” to isolate Tehran and reimposed sanctions that were lifted under the deal, which curbed Iran’s nuclear activities. 

In recent months, the United States and its allies have skirmished with Iranian forces in the Persian Gulf region, where Iran has sought to impede the passage of commercial tankers through the Strait of Hormuz.

In June, Iranian forces shot down a U.S. Navy spy drone over the strait, the world’s most important oil artery. Last month, U.S. forces also downed an Iranian spy plane and Iran’s Islamic Revolutionary Guard Corps detained a British-flagged tanker it said had “violated international maritime law.”

 The seizure was widely seen as a retaliatory action for Britain’s involvement in the detention of an Iranian oil tanker near Gibraltar on July 4. Local authorities said the vessel, which was carrying 2.1 million barrels of light crude oil, was suspected to be headed for the Syrian refinery at Baniyas, in violation of European Union sanctions. Iran denounced the ship’s seizure as an “act of piracy.”

“Whoever is starting the fire cannot be the firefighter,” Zarif said of the U.S. pressure campaign. “Every time that the U.S. has come to the Persian Gulf, it has brought nothing but violence and war.” 

But even as a potential conflict brews in the region, Trump has signaled that he is willing to negotiate with Tehran without preconditions. His administration says that Trump seeks a broader deal with Iran that would address its nuclear program, ballistic missile development and support for proxy forces in the Middle East.

Iranian officials have said that they will not negotiate with the United States as long as sanctions are in place.