An unarmed Iranian drone came within 100 feet (31 meters) of a U.S. Navy warplane as it prepared to land on an aircraft carrier in the Gulf, a U.S. official said on Tuesday.
"Despite repeated radio calls to stay clear of active fixed-wing flight operations in vicinity of the USS Nimitz, the QOM-1 executed unsafe and unprofessional altitude changes in the close vicinity of an F/A-18E," said a statement released by the U.S. Central Command.
"The dangerous maneuver by the QOM-1 ... created a collision hazard and is not in keeping with international maritime customs and laws," the Navy said. The U.S. jet had to manoeuvre to avoid a collision, with the two coming within 30 metres of each other.
Last month, a U.S. ship fired warning shots at an Iranian vessel that it said came too close during a military exercise. The U.S. Central Command's statement also noted that this occurrence was one of 13 "unsafe or unprofessional" interactions between the two countries' maritime forces in 2017.
Years of mutual animosity had eased when Washington lifted sanctions on Tehran last year as part of a deal to curb Iran's nuclear ambitions. But serious differences remain over Iran's ballistic missile program and conflicts in Syria and Iraq.
The Trump administration, which has struck a hard line on Iran, recently declared that Iran was complying with its nuclear agreement with world powers, but warned that Tehran was not following the spirit of the accord and that Washington would look for ways to strengthen it.
The United States has a number of military bases in the region, including in Qatar and Kuwait across the Gulf from Iran and the U.S. Fifth Fleet is based in nearby Bahrain.
Earlier this year, a senior commander in Iran's Revolutionary Guards warned the United States that if it designated the group a terrorist organization, its action could be perilous for U.S. forces in the region.