What we know and don't know about the U.S. drone-Russia jet collision

When a Russian fighter jet collided with a large U.S. surveillance drone over the Black Sea on Tuesday, it was a rare but serious incident that triggered a U.S. diplomatic protest and raised concerns about the possibility Russia could recover sensitive technology.

U.S. and Russian officials had conflicting accounts of the collision between the MQ-9 Reaper drone and the Russian Su-27 fighter jet — each blaming the other. A Pentagon spokesperson raised the possibility that the U.S. Defence Department could eventually declassify and release video it has of the collision.

Defence officials said the drone has not been recovered. But the Pentagon declined to say whether any effort was underway to gather debris or pieces of the Reaper.

Here's what's known — and uncertain — about the crash.

The Pentagon and U.S. European Command said that two Russian Su-27 aircraft dumped fuel on the MQ-9, which was conducting a routine surveillance mission over the Black Sea in international airspace. They said the Russian jets flew around and in front of the drone several times for 30 to 40 minutes, and then one of the Russian aircraft "struck the propeller of the MQ-9, causing U.S. forces to have to bring the MQ-9 down in international waters."

Air force Gen. James Hecker, commander of U.S. Air Forces Europe and Africa, said that the Russian jet's actions "nearly caused both aircraft to crash." Pentagon spokesperson Brig.-Gen. Pat Ryder said the collision likely also damaged the Russian fighter jet, but the Su-27 was able to land. He would not say where it landed.

The Pentagon said the drone was "well clear" of any Ukrainian territory, but did not provide details. A U.S. defence official said it was operating west of Crimea over the Black Sea. The official spoke on condition of anonymity to provide mission details.

It's not clear if the collision was an accident or intentional, but both sides agree the Russian aircraft were trying to intercept the drone.

The Russian Defence Ministry said the U.S. drone was flying near the Russian border and intruded in an area that was declared off-limits by Russian authorities. It said that the Russian military scrambled fighters to intercept the U.S. drone. It claimed that "as a result of sharp manoeuvre, the U.S. drone went into uncontrollable flight with a loss of altitude and collided with water surface."

Russia has declared broad areas near Crimea off limits to flights. Ever since the 2014 annexation of Crimea and long before Russia invaded Ukraine last year, Moscow has charged that U.S. surveillance planes were flying too close to its borders while ignoring the notices issued by Russia.

Nations routinely operate in international airspace and waters, and no country can claim limits on territory outside of its own border.

The ministry said the Russian aircraft were scrambled to intercept the drone but didn't use their weapons and "didn't come into contact" with it.

The MQ-9 Reaper is a large unmanned air force aircraft that is remotely operated by a two-person team. It includes a ground control station and satellite equipment and has a 20-metre wingspan. The team includes a rated pilot who is responsible for flying the aircraft and an enlisted aircrew member who is charged with operating the sensors and guiding weapons.

Used routinely during the Iraq and Afghanistan wars for surveillance and airstrikes, the Reaper can be either armed or unarmed. It can carry up to eight laser-guided missiles, including Hellfire missiles and other sophisticated munitions, and can loiter over targets for about 24 hours. It is about 11 metres long, 3.7 metres high and weighs about 2,200 kilograms. It can fly at an altitude of up to 15 kilometres and has a range of about 2,500 kilometres.