Russia has accused Ukraine of targeting Moscow in a drone attack after one smashed into a building causing a "powerful explosion".
It hit the Expo Center complex in central Moscow, which hosts conventions and conferences, in the early hours of Friday.
Russia's defence ministry and city mayor Sergei Sobyanin said there were no casualties after air defences shot down the unmanned drone which then fell on the building - situated about three miles from the Kremlin.
Footage circulating on social media purportedly shows the moment debris from the drone struck the building.
There is a small explosion followed by smoke billowing from the structure.
Ukrainian interior ministry adviser Anton Gerashchenko posted the video - originally from the pro-Kremlin Mash Telegram channel - on social media platform X (formerly Twitter).
Read more: Ukraine war latest
Pictures showed armed police securing the site and investigators working near the damaged building.
A witness who was in the area described hearing "a powerful explosion".
"At about 4am Moscow time, the Kyiv regime launched another terrorist attack using an unmanned aerial vehicle on objects located in Moscow and the Moscow region," the Russian defence ministry said.
There was no immediate comment from Kyiv.
Flights were briefly suspended at the four major airports around the capital - Vnukovo, Domodedovo, Sheremetyevo and Zhukovsky - which later reopened.
Drone air strikes deep inside Russia have increased since a drone was destroyed over the Kremlin in May.
Both Ukraine and Russia have denied targeting civilians during the conflict.
However, Russian President Vladimir Putin is wanted by the International Criminal Court over allegations of child abductions during the war - and Ukraine claims his forces have committed war crimes during the invasion.
Rise in attacks by Ukraine as Russia targets grain
The reported drone attack came hours after Russia's defence ministry claimed a separate attempted assault on its Black Sea fleet.
The ministry said two Russian warships repelled a Ukrainian attack with an unmanned boat near Crimea last night.
Patrol ships Pytlivy and Vasili Bykov reportedly fired at the Ukrainian boat and destroyed it.
Meanwhile, officials in Ukraine's southern Odesa region accused Russia of resuming its targeting of grain infrastructure.
Drones were used in overnight strikes on storage facilities and ports along the Danube River which Kyiv has increasingly used to transport grain to Europe after Moscow broke off a key wartime export deal through the Black Sea.
Odesa governor Oleh Kiper said air defences managed to intercept 13 drones.
At the same time, a loaded container ship stuck at the port of Odesa since the start of Russia's invasion of Ukraine in February last year set sail and was heading through the Black Sea to the Bosphorus along a temporary corridor established by Ukraine for merchant shipping.
It comes as Washington approved sending modern F-16 fighter jets to Ukraine from Denmark and the Netherlands as soon as the pilots are trained.
US Secretary of State Antony Blinken wrote to his Danish and Dutch counterparts saying "it remains critical that Ukraine is able to defend itself against ongoing Russian aggression and violation of its sovereignty".