Russia accused Kyiv of "terrorism" saying that two Ukrainian drones had damaged buildings in Moscow, including one close to the Defence Ministry's headquarters, a day after Ukraine promised payback for Russian strikes on Odesa.
Nobody was reported hurt in the attack, but one of its targets - close to the Moscow building where the Russian military holds briefings on what it calls its "special military operation" - struck a symbolic blow and underscored the reach of such drones.
Roads nearby were temporarily closed, windows on the top two floors of an office building struck by the second drone in another Moscow district were blown out, and debris was scattered on the ground, a Reuters reporter who saw the aftermath of the incident said.
"I was asleep and was woken up by a blast, everything started shaking," Polina, a young woman who lives near the high-rise building, told Reuters.
The Kremlin noted that the drones had been "neutralised" and vowed to press on with its operation in Ukraine and meet all of the aims of what Ukraine says is a brutal war of conquest.
The drone attack, though not serious in terms of its human cost or damage, was the most high-profile of its kind since two drones reached the Kremlin in May.
A swarm of 17 drones also launched attacks overnight on Crimea, which Russia annexed from Ukraine in 2014, the Russian Defence Ministry said, adding it had used anti-drone equipment and air defences to bring them down.
The Russian-installed head of Crimea said an ammunition warehouse had been struck and a residential building damaged.
Ukrainian President Volodymyr Zelensky, who rarely comments on attacks inside Russia or on Russian-controlled territory, had yesterday promised what he called "a retaliation to Russian terrorists for Odesa".
That was a reference to days of Russian missile strikes against targets in the port city which Moscow says are payback for a Ukrainian attack last week on the Crimean Bridge which killed the parents of a 14-year-old girl.
'Act of terrorism'
Writing on the Telegram messaging app, Ukrainian Deputy Prime Minister Mykhailo Fedorov mentioned the drone attacks.
"Electronic warfare and air defence are already less able to defend the skies of the occupiers."
Mr Fedorov, one of the officials spearheading Ukrainian efforts to create an 'army of drones', added: "No matter what happens there will be more of this."
Russia's defence ministry said its forces had used radio-electronic equipment to take out the two Ukrainian drones, forcing them to crash, thereby foiling what it called an attempted "terrorist attack".
Russian Foreign Ministry spokeswoman Maria Zakharova told the RTVI TV channel Ukraine was guilty of what she called "an act of international terrorism".
Moscow Mayor Sergei Sobyanin said on his Telegram messaging app that two non-residential buildings were struck at around 4am local time, adding there was no serious damage or casualties.
Citing emergency services, Russian state news agencies reported that drone fragments had been found near a building on Komsomolsky Avenue, which runs through Moscow.
The site is about 2km from the defence ministry's buildings.
Other military buildings, including some affiliated to Russia's GRU military intelligence service, are located nearby.
Traffic was temporarily closed on the street as well as on Likhachev Avenue, where a high-rise office building had been damaged, Russian news agencies reported.
Attention is now likely to turn to where the drones were launched from and whether pro-Ukrainian saboteurs inside Russia had a role.
After May's drone attack on the Kremlin, US drone experts concluded they might have been launched from inside Russia.
