MOSCOW (AP) — Russian officials accused Ukraine of targeting six Russian regions with drones early Wednesday in what appears to be the biggest drone attack on Russian soil since Moscow sent troops into Ukraine 18 months ago.

Drones hit an airport in the western Pskov region and started a massive fire there, the local governor and media reported. According to the Defense Ministry, more drones were also shot down over the regions of Oryol, Bryansk, Ryazan, Kaluga and the Moscow region surrounding the Russian capital.

The strike in Pskov hit an airport in the region's namesake capital and damaged four Il-78 transport aircraft, Russia’s state news agency Tass reported, citing emergency officials.

Pskov regional Gov. Mikhail Vedernikov ordered all flights to and from the Pskov airport canceled Wednesday, citing the need to assess the damage during daylight.

Footage and images posted on social media overnight showed smoke billowing over the city of Pskov and a large blaze. Vedernikov said there were no casualties, and the fire has been contained.

Pskov appeared to be the only region where the drones caused damage. Three drones were shot down over the Bryansk region, according to the Russian military, and two over the Oryol region, its Gov. Andrei Klychkov said. One was downed over the Ryazan region, one more over Kaluga, and one more over the Moscow region, officials said. No damage or casualties were registered in those regions.