The United States has denied a visa to Iranian Foreign Minister Mohammad Javad Zarif that would have allowed him to attend a United Nations Security Council meeting in New York on Thursday.

Monday"s comments by the official, who spoke on condition of anonymity, came as tensions escalate between the two countries after the US 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.”

U.N. spokesman Stephane Dujarric declined to comment on the U.S. denial of a visa for Zarif.