MOSCOW (AP) — Russian officials accused Ukraine of targeting six Russian regions early Wednesday in what appeared 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 governor and local media reported. More drones were shot down over Oryol, Bryansk, Ryazan, Kaluga and the Moscow region surrounding the Russian capital, according to the Defense Ministry.

The strike in Pskov, which was first reported minutes before midnight, hit an airport in the region’s namesake capital and damaged four Il-76 transport aircraft, Russia’s state news agency Tass reported, citing emergency officials.

Pskov regional Gov. Mikhail Vedernikov ordered all flights to and from the airport canceled Wednesday so damage could be assessed during daylight.

Footage and images posted on social media showed smoke billowing over the city of Pskov and a large blaze. Vedernikov said there were no casualties, and the fire has been contained. Unconfirmed media reports said between 10 and 20 drones could have attacked the airport.

Pskov was the main region where officials reported damage. In Kaluga, one drone was brought down and another hit an empty oil reservoir, causing a fire that was quickly extinguished, region Gov. Vladislav Shapsha reported. Residential windows were shattered, Shapsha said.

Three drones were shot down over the Bryansk region, according to the Russian military, and some Russian media cited residents as saying they heard a loud explosion. Two drones were downed over the Oryol region, its Gov. Andrei Klychkov said. Two more were downed over the Ryazan region and one over the Moscow region, officials said.

Outside Moscow, three main airports — Sheremetyevo, Vnukovo and Domodedovo — temporarily halted all incoming and outgoing flights, a measure that has become routine in the wake of the drone attacks.

There was no immediate comment from Ukrainian officials, who usually refuse to take responsibility for any attacks on the Russian soil.

Also early Wednesday, Russian-installed officials in the annexed Crimea reported repelling an attack of drones targeting the harbor of the port city of Sevastopol. Moscow-appointed governor of Sevastopol Mikhail Razvozzhayev said it wasn’t immediately clear how many of the drones have been destroyed. It wasn’t immediately clear if the attack caused any damage.

Drone attacks on Crimea or Russian regions have become increasingly common in recent months, with Moscow being a frequent target, as well as regions that border with Ukraine, such as Bryansk. Fuel depots and air fields have been hit in drone attacks Russian officials blamed on Kyiv.

The Oryol and Kaluga regions border with Bryansk, and the Moscow region sits on top of Kaluga. Pskov, however, is about 700 kilometers (434 miles) north of Russia’s border with Ukraine, near the border with Estonia and Latvia, and has been described by Russian media and military bloggers on Wednesday morning as an unlikely target.

In Ukraine in the meantime, media reported explosions in the southern city of Odesa, the Cherkasy region and in Kyiv. Kyiv Mayor Vitali Klitschko said debris fell on two districts of the capital, without clarifying whether that was the debris of a missile, or drone, or both.