A U.S. official says that an Iranian surface-to-air missile shot down a U.S. drone flying in international airspace over the Strait of Hormuz.

The official spoke to The Associated Press on Thursday on condition of anonymity as the information had yet to be cleared for release to the public.

Iran’s Revolutionary Guard said Thursday it shot down a U.S. drone amid heightened tensions between Tehran and Washington over its collapsing nuclear deal.

It said the U.S. drone was flying in Iranian airspace, contradicting the U.S. official.

The reported downing of the RQ-4 Global Hawk comes after the U.S. military previously alleged Iran fired a missile at another drone last week that responded to the attack on two oil tankers near the Gulf of Oman. The U.S. blames Iran for the attack on the ships, something Tehran denies.