WASHINGTON, Aug 23 (Reuters) - The United States does not encourage or enable attacks inside Russia, a U.S. State Department spokesperson said after Russian authorities said they downed drones that tried to attack Moscow early on Wednesday.

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

Drone strikes deep inside Russia have increased since two unmanned aircraft were destroyed over the Kremlin in early May. Drone strikes on the Russian capital have become increasingly common in recent months.

The United States, which has supplied Ukraine with massive assistance in the form of weapons and other military equipment to combat the Russian invasion, has consistently said it does not support attacks inside Russia.

The Russian defence ministry said early on Wednesday that air defence systems downed three drones that tried to attack Moscow.

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

Moscow airports suspended flights early on Wednesday, Russia's TASS news agency reported. Major airports around the Russian capital have repeatedly closed for departing and arriving flights in recent days due to Ukrainian drone activity.

Russia also shot down two Ukrainian drones over the Moscow region with no casualties and brought down a further two drones over the Bryansk region that borders Ukraine, the Defence Ministry said on Tuesday.

Ukraine typically does not comment on who is behind attacks on Russian territory 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 caused mostly minor damage to buildings.