The leader of Russia's Wagner Group mercenary force has said that he believes a promised counteroffensive by Ukrainian troops has begun and that his forces are observing heightened activity along the front.
In an audio message published by his press service on social media, Yevgeny Prigozhin said that the "active phase" of the operation would begin in the coming days.
The Kyiv government has long promised a counteroffensive to start taking back territory in the east that Russia annexed after invading in February 2022.
"I believe the advance of the Ukrainian army has already begun. We are seeing the greatest possible activity both on the perimeter and within the front lines," Mr Prigozhin said.
"I therefore believe that it has all already started. And I believe it will all enter an active phase in the very near future. It could be a matter of days."
Mr Prigozhin later said his forces had advanced 230 metres in fighting that has engulfed the eastern Ukrainian town of Bakhmut.
The shattered town, once home to 70,000, has been under siege for nearly ten months.
Mr Prigozhin said Ukrainian forces are now confined to an area in the town making up just 2.64sq/km.
He repeated his complaint that Moscow was ignoring his pleas to increase supplies of shells.
"The ministry of defence has not provided us with artillery ammunition and we only have resources for a few days. They ignore all requests from Wagner."
Earlier, Russia accused Ukraine of a failed attempt to assassinate President Vladimir Putin in a drone attack on the Kremlin in Moscow and threatened to retaliate.
Ukrainian President Volodymyr Zelensky said Kyiv had nothing to do with the reported incident.
"We don't attack Putin, or Moscow, we fight on our territory," Mr Zelensky told a press conference during a visit to Finland, alluding to Russian forces that swept into Ukraine last year.
A senior aide to the president called the accusation a sign that Russia was planning a major new attack on Ukraine.
Shortly after Moscow's announcement, Ukraine reported alerts for air strikes over the capital Kyiv and other cities.
Russia said that two unmanned aerial vehicles were aimed at the Kremlin.
"As a result of timely actions taken by the military and special services with the use of radar warfare systems, the devices were put out of action," a statement said.
"We regard these actions as a planned terrorist act and an attempt on the president's life, carried out on the eve of Victory Day, the May 9 Parade, at which the presence of foreign guests is also planned."
Fragments of drones were scattered in the Kremlin grounds but there were no injuries or damage, it said.
President Putin himself was safe.
"The Russian side reserves the right to take retaliatory measures where and when it sees fit," the statement said.
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Video posted by Baza, a Telegram channel with links to Russia's law enforcement agencies, showed a flying object approaching the dome of a Kremlin building overlooking Red Square, exploding in a burst of light just before reaching it.
Other video posted on a neighbourhood internet group showed a plume of smoke over the Kremlin's gold domes.
The videos could not be independently verified.
In comments sent to the Reuters news agency, Ukrainian presidential adviser Mykhailo Podolyak said Kyiv was not involved in the incident.
"We do not attack the Kremlin because, first of all, it does not resolve any military tasks."
Mr Podolyak said the accusation, along with an announcement that Russia had caught suspected saboteurs in Ukraine's Russian-occupied Crimea region, "clearly indicates the preparation of a large scale terrorist provocation by Russia in the coming days".
Vyacheslav Volodin, the influential speaker of Russia's parliament, demanded the use of "weapons capable of stopping and destroying the Kyiv terrorist regime" in response to the alleged drone attack on the Kremlin.
Former Russian president Dmitry Medvedev called for the "physical elimination" of President Zelensky in the wake of the incident.
"After today's terrorist attack, there are no options left aside the physical elimination of Zelensky and his cabal," Mr Medvedev said.
US Secretary of State Antony Blinken, in remarks quoted by the Washington Post, said the United States was unable to validate reports of the drone strike, but that he would regard anything coming from the Kremlin "with a very large shaker of salt".
Elsewhere, oil depots were ablaze in southern Russia and Ukraine, as both sides escalated a drone war ahead of Kyiv's promised spring counteroffensive against Russian forces.
Scores of firefighters battled a huge fire that Russian authorities blamed on a Ukrainian drone crashing into an oil terminal on Russia's side of its bridge to Crimea.
A fuel depot in Ukraine was ablaze after a suspected Russian drone strike on the central city of Kropyvnytskyi.
An administrative building in Ukraine's southern Dnipropetrovsk region was also hit by a drone and set ablaze.
Ukraine said it had shot down 21 of 26 Iranian-made drones in an overnight volley, shielding targets in Kyiv where air raid sirens blared for hours through the night.
Russian shelling killed 21 civilians in and near the southern Ukrainian city of Kherson today, including strikes on a supermarket, a railway station and crossing, a petrol station and residential buildings, President Zelensky said.
Forty-eight people were known to have been injured, he added on the Telegram messaging app.
"All civilians! With the day not yet over! In one region!" he wrote.
Russian forces have regularly shelled the city from parts of the region occupied by Russia.
Moscow says it has struck military targets, though it has produced no evidence to support this.
In videos posted on Russian social media of the burning fuel depot near the Crimea bridge, flames and black smoke billowed over large tanks emblazoned with red warnings of "Flammable".
In Ukraine, the governor of the central Kirovohrad region said three Russian drones had targeted an oil facility in the region's main city Kropyvnytskyi. Prosecutors said a huge blaze had broken out there.
President Zelensky visited Finland today, his fourth known trip abroad since Russia's full-scale invasion.
Leaders of Denmark, Iceland, Norway and Sweden also attended his visit.
He said his goals were to beef up Ukraine's military and secure an eventual place in the NATO alliance, a goal endorsed by the five Nordic nations in a statement.
President Zelensky is set to make a visit to the Netherlands tomorrow, where he will deliver a speech and will have meetings with Prime Minister Mark Rutte and members of parliament, the Dutch government said.
In Brussels, European Union countries finalised a €1 billion scheme to jointly buy ammunition and missiles for Ukraine after weeks of wrangling.
Russia says it launched its "special military operation" to counter a threat from Kyiv's relations with the West.
Ukraine and its allies call it an unprovoked war of conquest by Moscow, derailed by a failed assault on the capital Kyiv early last year and Ukrainian advances in the second half of 2022.
Over the past five months, Ukrainian ground forces have kept mostly to the defensive, while Russia launched a huge, largely unsuccessful winter assault, capturing little new ground.
