An Iranian drone that flew over a U.S. aircraft carrier last month was the first to conduct an overflight of an American carrier since 2014, according to a U.S. Navy report obtained by The Associated Press on Wednesday.

The Jan. 12 reconnaissance flight by the Iranian Shahed drone was the latest in a series of tense naval encounters between forces of the Islamic Republic and the U.S. Navy, including the brief detention of 10 American sailors who strayed into Iranian territorial waters in the Persian Gulf.

All the incidents have come after Iran signed a nuclear deal with world powers including the U.S., and point to lingering tensions between the two playing out in key waterways used to transport oil.

An internal U.S. Navy report on the incident, obtained by the AP through a Freedom of Information Act request, said it happened as the USS Harry S. Truman and the French aircraft carrier Charles de Gaulle were 89 nautical miles southwest of the Iranian port of Bushehr.

The U.S. Navy dispatched a Seahawk helicopter to observe the Shahed-121 drone as it flew over the Truman, a nuclear-powered carrier based out of Norfolk, Virginia. “Shahed” means “witness” in both Farsi and Arabic.

The U.S. Navy taskforce in the area publicly described the drone’s overflight as “safe, routine and professional.” But the internal report says the Navy’s higher command described it as “safe, abnormal and unprofessional,” as Iranian drones seldom fly over American carriers.

U.S. and French sailors repeatedly confirmed that the Iranian drone had its “wings clean,” the report said. That means it did not carry weapons and didn’t pose a risk to the ship, said Cmdr. Kevin Stephens, a spokesman for the U.S. Navy’s 5th Fleet based in Bahrain.

“They’re operating in international airspace. You can’t shoot (it) down; that would be illegal,” Stephens said.

Iran’s Revolutionary Guard is using similar Shahed-129 drones as ground support to forces fighting on the side of President Bashar Assad in Syria, the semi-official Fars news agency reported last week. The difference between the two models was not immediately clear. Iran also said it deployed Shahed drones during war games near the Iranian holy city of Qom that simulated a capture of Jerusalem’s Al-Aqsa Mosque in November.

The last drone overflight of an American aircraft carrier happened in September 2014 and involved the USS George H.W. Bush, according to the report. That happened as the U.S. and other world powers were in the midst of negotiating a final agreement over the fate of Iran’s disputed nuclear program. An interim agreement had been reached to limit the program the previous year, but neither side had been able to finalize the deal by a June 2014 deadline, leading talks to be extended.

In January, Iranian state television aired footage it said came from a drone overflight. The footage, which the AP could not independently verify, purported to show the drone being launched and then hovering over an unidentified aircraft carrier, a targeting bracket briefly passing over a jet parked on the deck below.

Iran has more than 2,000 kilometers (1,240 miles) of shoreline facing the Persian Gulf and the Sea of Oman. Control of that territory, including the Strait of Hormuz, through which nearly a third of all oil traded by sea passes, has remained a priority for Iran’s military, and it conducts regular drills in the region.

The U.S. has criticized some of those maneuvers, including what it called a “highly provocative” Iranian rocket test in December near U.S. warships and commercial traffic passing through the strait.

(AP)