Ukraine on Monday claimed a drone attack in central Moscow, the latest in a series of strikes revealing Russian vulnerabilities, while Kyiv said Russian forces again hit grain facilities near Odesa.
Russia last week pulled out of a key deal which had allowed the safe export of Ukrainian grain through the Black Sea, and since then Kyiv has accused Russia of targeting grain supplies and infrastructure.
In Moscow, police cordoned off streets near the defence ministry where a drone crashed, while the second shattered glass walls of an office building in a southern district.
A Ukrainian defence source told AFP that the attack -- one day after Kyiv vowed to retaliate for a Russian missile strike in the city of Odesa -- was a "special operation" by Ukraine's military intelligence.
Russia said that the attacks could warrant "tough retaliatory measures."
"We regard what happened as yet another use of terrorist methods and intimidation of the civilian population," Russia's foreign ministry added.
AFP reporters at the scene of the strike near the ministry saw a two-storey building with its roof torn apart by the impact of the drone's crash.
"It was 3:39am. The house really shook," said Vladimir, 70, who lives nearby. "It is scandalous that a Ukrainian drone almost flew into the defence ministry."
In Crimea, the peninsula annexed by Russia in 2014, Moscow-installed governor Sergei Aksyonov said an ammunition depot had also been hit in by drones.
Meanwhile, in Ukraine's Odesa region, officials reported a four-hour Russian drone attack on port infrastructure on the Danube River.
"A grain hangar was destroyed and tanks for storing other types of cargo were damaged," Ukraine's southern military command said on Telegram.
The Danube delta region, which spans across Romania and Ukraine, is being used as an export route for Ukrainian grain -- a key factor in the conflict.
- Grain tensions -
In June, Brussels agreed to allow Poland, Bulgaria, Hungary, Slovakia and Romania to restrict imports of grain from Ukraine through September.
But Ukrainian President Volodymyr Zelensky on Monday branded as "unacceptable" any move by the European Union to extend the curbs to protect local farmers who fear being undercut.
Also on Monday, a child was killed and six people wounded in a Russian strike on the east Ukraine city of Kostiantynivka, the region's governor said.
In a separate incident, an AFP video journalist was wounded by a drone attack while reporting at a Ukrainian artillery position.
Dylan Collins, a US citizen, sustained multiple shrapnel injuries in the attack in a forested area near Bakhmut. He was evacuated to a nearby hospital and doctors have said his condition was not life-threatening.
Kyiv meanwhile said it had recaptured over 16 square kilometres of territory from Russian forces last week in the east and south, nearly two months into its highly-anticipated counteroffensive.
On Sunday, a Russian strike on Odesa killed two people and severely damaged a historic cathedral.
Clergymen rescued icons from rubble inside the Transfiguration Cathedral, which was demolished under Stalin in 1936 and rebuilt in the 1990s after the collapse of the Soviet Union.
The Ukrainian government condemned the cathedral strike as a "war crime", saying it had been "destroyed twice: by Stalin and Putin".
The Kremlin blamed the damage on Ukraine's air defence systems.
The prolonged conflict has drawn in neighbouring states, and staunch Russian ally Belarus said Monday it was reviewing security with members of Russia's Wagner mercenaries after their failed uprising back home.
Interior Minister Ivan Kubrakov met Wagner commanders at a training centre to draw up a "clear plan of action", a statement said.
Belarus President Alexander Lukashenko is hosting the fighters after brokering a deal that convinced their leader Yevgeny Prigozhin to end a June march on Moscow and exile himself in Belarus.