TEHRAN, Iran (AP) — Iran’s Revolutionary Guard shot down a U.S. drone today amid heightened tensions between Tehran and Washington over its collapsing nuclear deal with world powers, American and Iranian officials said, while disputing the circumstances of the incident.

The Guard said it shot down the drone over Iranian airspace, while two U.S. officials told The Associated Press that the downing happened over international airspace in the Strait of Hormuz. The different accounts could not be immediately reconciled.

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. The White House separately said it was aware of reports of a missile strike on Saudi Arabia amid a campaign targeting the kingdom by Yemen’s Iranian-allied Houthi rebels.

Iran recently quadrupled its production of low-enriched uranium and threatened to boost its enrichment closer to weapons-grade levels, trying to pressure Europe for new terms to the 2015 nuclear deal.

In recent weeks, the U.S. has sped an aircraft carrier to the Mideast and deployed additional troops to the tens of thousands already in the region. From Yemen, the Houthis have launched bomb-laden drones into neighboring Saudi Arabia.

All this has raised fears that a miscalculation or further rise in tensions could push the U.S. and Iran into an open conflict.