The United States does not encourage or permit attacks inside Russiaa State Department spokesman said after Russian authorities said they had shot down drones that tried to attack Moscow early Wednesday, according to a Reuters report.

It is up to Ukraine to decide how it chooses to defend itself from the Russian invasion, which began in February last year, the State Department spokesman said, adding that Russia could end the war at any time by withdrawing from Ukraine .

The attacks with drones deep inside Russia have increased since two drones were shot down over the Kremlin in early May. Drone raids on the Russian capital have become increasingly frequent in recent months.

The United States, which has provided Ukraine with massive aid in the form of weapons and other military equipment, has consistently said it does not support attacks inside Russia.

The Russian Defense Ministry announced early Wednesday that air defense systems shot down three drones that attempted to attack Moscow.

A drone struck a building under construction in central Moscow early Wednesday, Moscow Mayor Sergei Sobyanin said on his Telegram channel, a messaging app.

Moscow airports suspended flights early Wednesday, Russian news agency TASS reported. Major airports around the Russian capital have been repeatedly closed to departing and arriving flights in recent days due to Ukrainian drones.

Russia also shot down two Ukrainian drones over the Moscow region without casualties and shot down two more drones over the Bryansk region bordering Ukraine, the defense ministry said on Tuesday.

Ukraine does not usually comment on who is behind attacks on Russian soil, but it appears to have stepped up such raids since two drones were destroyed over the Kremlin in early May.

Such attacks have briefly disrupted flights and mostly caused minor damage to buildings.