Crew on board the U.S. Navy’s amphibious assault ship USS Boxer has brought down an Iranian drone near the Strait of Hormuz, the Department of Defense and President Donald Trump said on Thursday.

“At approximately 10 a.m. local time, the amphibious ship USS Boxer was in international waters conducting a planned inbound transit of the Strait of Hormuz,” Chief Pentagon Spokesperson Jonathan Hoffman said in a July 18 statement.

“A fixed wing unmanned aerial system (UAS) approached Boxer and closed within a threatening range. The ship took defensive action against the UAS to ensure the safety of the ship and its crew.”

The U.S. assesses that the drone was Iranian, Pentagon spokesperson CDR Rebecca Rebarich told The Defense Post.

U.S. Marines on board the Boxer brought down the drone with a Light Marine Air Defense Integrated System, or LMADIS, Military.com reported citing an American defense official.

The LMADIS is installed on MRZR all-terrain vehicles and uses radio frequencies to jam drones in flight. The system was still experimental as of May, having found use against Islamic State drones in Iraq and Syria, but testing was expected to end by the end of the year.

Speaking at the White House earlier on Thursday, Trump said the Boxer had brought down an Iranian drone “which had closed into a very, very near distance, approximately 1,000 yards, ignoring multiple calls to stand down, and was threatening the safety of the ship and the ship’s crew.”

“The drone was immediately destroyed,” he said.

On Friday, Iran’s deputy foreign minister Seyed Abbas Araghchi denied the Islamic Republic had lost a drone.

The Strait of Hormuz, which runs between the Persian Gulf and and Gulf of Oman, is a key shipping route for international commerce. The Boxer had entered the Strait about three hours earlier, according to reports.

Late Thursday the Wall Street Journal reported that a U.S. helicopter chased away an unarmed Iranian navy Bell 212 helicopter that flew close to the Boxer shortly after the ship had entered the Strait of Hormuz. A larger Iranian vessel, which the WSJ did not identify, at one point sailed as close as 500 yards to the Boxer, the report said.

The incident comes nearly a month after Iran’s Islamic Revolutionary Guard Corps shot down a U.S. RQ-4 Global Hawk surveillance drone which it said violated Iranian airspace in the Gulf of Oman. The U.S. maintains the drone was operating in international airspace.

Earlier on Thursday, Iran said it had seized an oil tanker carrying fuel that the Islamic Republic claims was being smuggled through the Persian Gulf.