Russia and the United States have offered different accounts of the downing of a US intelligence drone in the Black Sea.
Below are the two accounts.
What the United States said:
The United States announced on Tuesday that one of its MQ-9 'Reaper' intelligence and surveillance drones had been struck by a Russian Su-27 fighter.
According to the US Department of Defence, the Russian fighter hit the drone's propeller and forced US forces to bring the drone down.
"Several times before the collision, the Su-27s dumped fuel on, and flew in front of the MQ-9 in a reckless, environmentally unsound and unprofessional manner," James B. Hecker, commander of US Air Forces Europe and Air Forces Africa, said.
"This incident demonstrates a lack of competence in addition to being unsafe and unprofessional," Mr Hecker said.
The United States said the drone was conducting routine operations in international airspace when it was intercepted and hit by the Russian aircraft.
What Russia said:
Russia said the MQ-9 drone was flying near Crimea – which Russia annexed in 2014 – and heading towards territories which Russia considers its own.
"As a result of sharp manoeuvring, the MQ-9 unmanned aerial vehicle went into an uncontrolled flight with a loss of altitude and collided with the water," Russia's defence ministry said.
Russia said the transponders of the drone had been turned off and that fighters had been scrambled to identify it.
"Russian fighters did not use airborne weapons, did not come into contact with the unmanned aerial vehicle and returned safely to the home airfield."
Russia's ambassador to the United States, Anatoly Antonov said the drone's fight was unacceptable.
"The unacceptable actions of the United States military in the close proximity to our borders are cause for concern," Mr Antonov said.
"We are well aware of the missions such reconnaissance and strike drones are used for."
"If, for example, a Russian strike drone appeared near New York or San Francisco, how would the US Air Force and Navy react?" Mr Antonov asked.
He said the United States should stop flying drones so close to "Russian borders".
What is the MQ-9 Reaper drone?
According to the US Air Force, the Reaper is "employed primarily as an intelligence-collection asset and secondarily against dynamic execution targets".
"Given its significant loiter time, wide-range sensors, multi-mode communications suite, and precision weapons, it provides a unique capability to perform strike, coordination, and reconnaissance against high-value, fleeting, and time-sensitive targets," the air force said.
"Reapers can also perform the following missions and tasks: intelligence, surveillance and reconnaissance, close air support, combat search and rescue, precision strike, buddy-lase, convoy and raid overwatch, route clearance, target development, and terminal air guidance.
"The MQ-9's capabilities make it uniquely qualified to conduct irregular warfare operations in support of combatant commander objectives."