Moscow claims Ukraine has carried out a string of drone attacks in southern and western Russia.
The flurry of drones overnight on Monday and into Tuesday were said to be aimed at regions inside Russia along the border with Ukraine and deep into the country.
At the same time, the hacking of Russian TV channels and radio stations, as well as the temporary closure of Saint Petersburg’s airport, fuelled suspicion that Kyiv could be behind the disruption.
One of the drones crashed just 100km from Moscow, according to local authorities, who said it had probably been intended to attack civil infrastructure.
It fell near a gas distribution station close to the city of Kolomna, 110km south-east of the capital, according to the RIA Novosti news agency.
There was no damage to infrastructure and no casualties were reported, the regional governor said.
It came after the defence ministry claimed Ukraine launched drone attacks against two southern Russian regions overnight.
The attacks — in the Krasnodar and Adygea regions — had been “suppressed” and failed to inflict any damage, it said.
But it followed reports by Russian state news agencies of a fire at an oil depot in Krasnodar, around 240km south-east of the Crimean peninsula, after a drone was spotted flying overhead.
“The Kyiv regime attempted to use unmanned aerial vehicles to attack civilian infrastructure in the Krasnodar region and the Adygea Republic,” the Russian defence ministry said.
“The UAVs were neutralised by electronic warfare units.”
While Ukrainian drone strikes on the Russian border regions of Bryansk and Belgorod that lie north of Ukraine’s Sumy region are not unusual, the hits on the Krasnodar and Adygea regions further south are noteworthy.
Ukrainian authorities offered no immediate acknowledgement or comment on the reported strikes.
Last year, Russian authorities repeatedly reported shooting down Ukrainian drones over annexed Crimea. In December, the Russian military said Ukraine used drones to hit two bases for long-range bombers deep inside Russian territory.
Separately, the local government of Saint Petersburg — Russia’s second-largest city 1,300km north of the border with Ukraine — said on Tuesday that it was temporarily halting all flight departures and arrivals at the city’s main airport, Pulkovo. It did not give a reason for the move.
Hours earlier, unconfirmed reports on Russia's Telegram social network referred to the air space over the city being shut down and to Russian warplane overflights.
It was not immediately clear whether this was connected to the alleged rise in drone attacks in Russia’s south.
The Russian military said its air defence forces in western Russia conducted drills on “detection, interception and identification” of enemy targets in its air space, as well as in co-ordination with civilian air traffic services in an emergency situation.
The Russian Defence Ministry did not specifically mention Saint Petersburg, but its statement appeared designed to explain the temporary closure of the air space.
Kremlin spokesman Dmitry Peskov refused to comment on the situation in Saint Petersburg, urging reporters to wait for details from the country’s aviation authorities or the military.
He noted, however, that President Vladimir Putin had “full information” on the situation.
Speaking at Russia’s main security agency, the FSB, Mr Putin urged the service to tighten security on the border with Ukraine.
Russian media reported on Tuesday morning that in several Russian regions an air raid alarm interrupted the programming of several TV channels and radio stations.
Footage posted by some news sites showed TV sets displaying a yellow sign with a person heading to a bomb shelter, with a female voice repeating: “Attention! Air raid alarm. Everyone should head to a shelter immediately.”
Ukraine said on Tuesday that its troops were under pressure in the near-destroyed frontline city of Bakhmut, where Russian forces were launching heavy assaults after months of fighting.
The former eastern industrial hub has become largely a political objective since the longest battle in Russia's year-long invasion has already reduced it to rubble, causing high casualties on both sides.
Aerial footage shows almost all of Bakhmut's buildings in ruins and smoke rising over the city once known for its sparkling wine production and salt mines.
Meanwhile, Nato chief Jens Stoltenberg said on Tuesday that Ukraine will become a member of the alliance in the “long-term”.
But he stressed that the immediate issue is for it to remain an independent nation in the face of Russia's invasion.
“Nato allies have agreed that Ukraine will become a member of our alliance, but at the same time that is a long-term perspective,” Mr Stoltenberg told reporters during a visit to Finland's capital Helsinki.
He said “the issue now is that Ukraine prevails as a sovereign independent nation, and therefore we need to support Ukraine”.
After Russia's invasion, Ukraine's President Volodymyr Zelenskyy has urged the US-led military alliance to grant his country a fast-track membership.
Ukraine applied for EU membership in February 2022, shortly after it was invaded, and was granted candidate status in June.
When the war ends “we need to ensure that history doesn't repeat itself,” Mr Stoltenberg told a press conference with Finnish Prime Minister Sanna Marin.
“President Putin cannot continue to attack neighbours. He wants to control Ukraine and he is not planning for peace, he is planning for more war.”
Spooked by Moscow's invasion of Ukraine, Finland and Sweden dropped their decades-long policies of military non-alignment and applied to join Nato in May last year.
“I see that the future of Ukraine is to be part of the European Union and also a member of Nato,” Ms Marin added.
Turkey and Hungary are the only remaining members yet to ratify the Finnish and Swedish bids to join the alliance.
Mr Stoltenberg said that “both Finland and Sweden have delivered on what they promised in the trilateral agreement they made with Turkey last June in Madrid”.
“The time is now to ratify and to fully welcome Finland and Sweden as members,” he said.