Russia has denied Ukraine’s accusations that it is to blame for shooting down one of its fighter jets.
A Kiev military spokesman had said its neighbour was behind the attack, which took place in the east of Ukraine.
But Russia’s United Nations ambassador, Vitaly Churkin, was blunt, telling reporters: “We didn’t do it.”
Ukraine’s national security and defence council had claimed on Twitter: “A military plane from the air force of the Russian Federation carried out a rocket strike on a Ukrainian airforce (Sukhoi Su-25 Frogfoot fighter plane) as it fulfilled its task over the territory of Ukraine.”
The pilot of the downed fighter jet managed to eject and was later evacuated by Ukrainian forces, the military said.
It is the strongest Ukrainian allegation to date of direct Russian military involvement in the three-month conflict.
It also marks the third reported incident this week in which a Ukrainian plane has been hit by a missile.
Kiev said that an An-26 military transporter was brought down last Monday, likely by a missile fired from Russia.
Two out of the eight people on board that plane were killed.
Meanwhile on Wednesday, another Su-25 was hit by a rebel missile but the pilot brought the plane down successfully.
Kiev did not allege Russian involvement in that case.
Moscow denies orchestrating rebellion in eastern Ukraine, but Western governments accuse it of failing to do enough to curb the violence.