NEW YORK (TicToc by Bloomberg) — Iran’s Revolutionary Guard shot down a U.S. surveillance drone on Thursday amid heightened tensions between Tehran and Washington over the collapsing nuclear deal with world powers, American and Iranian officials said, though they disputed the circumstances of the incident.

The Guard said it shot down the RQ-4 Global Hawk drone over Iranian airspace, while the U.S. said the downing happened over international airspace in the Strait of Hormuz. The different accounts could not be immediately reconciled.

The U.S. military’s Central Command called it an “unprovoked attack” and President Donald Trump tweeted that “Iran made a very big mistake” in shooting it down. Previously, the U.S. military alleged that Iran had fired a missile at another drone last week that was responding to the attack on two oil tankers near the Gulf of Oman. The U.S. blames Iran for the attack on the ships; Tehran denies it was involved.

The attacks come against the backdrop of heightened tensions between the U.S. and Iran following President Donald Trump’s decision to withdraw from Tehran’s nuclear deal a year ago.

Separately, Saudi Arabia said on Thursday that Yemen’s Iranian-allied Houthi rebels launched a rocket targeting a desalination plant in the kingdom the previous night. The White House said Trump was briefed about that attack.

Iran’s state-run IRNA news agency, citing the Guard, identified the drone as an RQ-4 Global Hawk, which cost over $100 mln apiece and can fly higher than 16 km and stay in the air for over 24 hours at a time. They have a distinguishable hump-shaped front and an engine atop. Their wingspan is bigger than a Boeing 737 passenger jet.

The Guard described the drone as being launched from the southern Persian Gulf but did not elaborate. U.S. RQ-4 Global Hawks are stationed at the Al-Dhafra Air Base in the United Arab Emirates, near the capital, Abu Dhabi. AP journalists saw the drones on the base’s tarmac during a March 2016 visit by then-Vice President Joe Biden.

The CENTCOM statement said the RQ-4A Global Hawk maritime surveillance drone was shot down by an Iranian surface-to-air missile while in international airspace over the Strait of Hormuz, the narrow mouth of the Persian Gulf through which 20% of all global oil moves.