Monday’s comments by the official, who spoke on condition of anonymity, came as tensions escalate between the two countries after the United States killed Iran’s most prominent military commander, Qassem Soleimani, in Baghdad on Friday.

Under the 1947 U.N. “headquarters agreement,” the United States is generally required to allow access to the United Nations for foreign diplomats. But Washington says it can deny visas for “security, terrorism and foreign policy” reasons.

The U.S. State Department declined immediate comment. Iran’s mission to the United Nations said: “We have seen the media reports, but we have not received any official communication from either the U.S. or the U.N. regarding Foreign Minister Zarif’s visa.”