Russia claims the United States was behind what it says was a drone attack on the Kremlin that aimed to kill President Vladimir Putin.
It came as Moscow's forces fired more combat drones at Ukrainian cities on Thursday, including the capital, Kyiv, following missile strikes on the city of Kherson on Wednesday which killed 23 people.
Mr Putin's spokesman Dmitry Peskov, without providing evidence, said Ukraine had acted on US orders when it launched what Russia said was a drone attack on the Kremlin building in the early hours of Wednesday morning.
"We know very well that decisions about such actions, about such terrorist attacks, are made not in Kyiv but in Washington," Mr Peskov said.
White House national security spokesman John Kirby said Mr Peskov's claims were false, and the United States did not encourage or enable Ukraine to strike outside its borders.
"I can assure you that there was no involvement by the United States in this. Whatever it was did not involve us," Mr Kirby told cable news network MSNBC.
"We still don't really know what happened."
Kyiv also denied involvement in the incident, which followed a string of explosions over the past week targeting freight trains and oil depots in western Russia and Russian-controlled Crimea.
Shelling kills 23, injures 46 in Kherson
Russian shelling killed 23 people in and near the southern Ukrainian city of Kherson on Wednesday, hitting a hypermarket, a railway station and residential buildings, the regional governor said.
"The enemy's targets are the places where we live. Their targets are our lives, and the lives of our children," governor Oleksandr Prokudin said, announcing the latest death toll in an online video on Thursday.
President Volodymyr Zelenskyy on Wednesday denounced the attacks on Kherson, condemning "the bloody trail that Russia leaves behind with its shells".
Mr Prokudin said 46 people had also been wounded in Wednesday's attacks.
The dead included three engineers trying to repair damage inflicted on the power grid in earlier Russian bombardments, local officials said.
Pools of blood and piles of debris lay on the ground outside the Kherson hypermarket after the attacks, Reuters correspondents on the scene said.
Russia did not immediately comment on the attacks in Kherson, one of four Ukrainian regions it said it annexed last September. Moscow has denied targeting civilians in its invasion of Ukraine.
Moscow has stepped up air strikes on Ukraine in the past few days, as Kyiv prepares for a counteroffensive in which it is expected to try to retake occupied territory in the Kherson region.
Ukrainian troops recaptured Kherson city last November after nearly eight months of occupation, but Russian troops retreated only as far as the opposite side of the Dnipro River, from where they now shell the city.
Explosions heard in Kyiv, Zaporizhzhia
Shortly after the news out of Kherson, explosions were also heard in the Ukrainian capital Kyiv and several other cities, with some local authorities reporting that anti-aircraft defences were at work.
Reuters eyewitnesses in the capital said there had been at least one loud blast, while Ukrainian public broadcaster Suspilne reported explosions in the southern city of Zaporizhzhia.
Local media also reported blasts in the Black Sea port of Odesa. Air alerts were sounded in most of the eastern half of the country, according to an official government map.
Zelenskyy visits The Hague, meets with ICC president
Russian President Vladimir Putin must be brought to justice for the war, Mr Zelenskyy said on Thursday during a visit to The Hague, where the International Criminal Court (ICC) is based.
The ICC in March issued an arrest warrant for Mr Putin for the suspected deportation of children from Ukraine.
"We all want to see a different Vladimir here in The Hague, the one who deserves to be sanctioned for his criminal actions here, in the capital of international law," Mr Zelenskyy said in a speech, referring to Mr Putin.
"I'm sure we will see that happen when we win," he said, adding: "Whoever brings war must receive judgement."
Russia, which is not a member of the ICC and rejects its jurisdiction, denies committing atrocities during its conflict with Ukraine, which it terms a "special military operation".
The Ukrainian president, dressed in his trademark khaki T-shirt and trousers, was welcomed at the court earlier in the day by its president, judge Piotr Hofmanski.
The ICC said the visit lasted less than an hour, but gave no details on what was discussed.
As he left, Mr Zelenskyy waved at a Ukrainian family standing outside the ICC building as they shouted "Slava Ukraini" — or "Glory to Ukraine".
The Ukrainian leader has visited several foreign capitals including London, Paris and Washington since Russia's 2022 invasion.
The Netherlands has been a strong supporter of Ukraine, with Prime Minister Mark Rutte in February saying he did not rule out any kind of military support for Kyiv as long as it did not bring NATO into conflict with Russia.
European Commission chief Ursula von der Leyen said in February that an international centre for the prosecution of the crime of aggression in Ukraine would be set up in The Hague.
The ICC can prosecute genocide in Ukraine, but has no jurisdiction over alleged crimes of aggression by Russia there.
An act of aggression is defined by the United Nations as the "invasion or attack by the armed forces of a state [on] the territory of another state, or any military occupation".
Drones attack Russian oil refinery
A day after the alleged drone strike on the Kremlin, a drone attack set fire to product storage facilities at one of the largest oil refineries in southern Russia on Thursday.
Emergency services extinguished the fire just over two hours later, Russia's state TASS news agency reported.
The Ilsky refinery, near the Black Sea port of Novorossiisk in the Krasnodar region, has a processing capacity of around 6.6 million tonnes per year.
"The consequences of the incident were eliminated," the news agency reported, citing the plant's press service.
A day earlier, a fuel depot further to the west caught fire near a bridge linking Russia's mainland with the occupied Crimea peninsula.
"A second turbulent night for our emergency services," Krasnodar governor Veniamin Kondratyev wrote on Telegram, adding that there were no casualties.
Ukraine rarely claims responsibility for what Moscow says are frequent drone strikes against infrastructure and military targets, particularly in regions close to Russia.
Moscow blamed Ukraine for an attack on April 29 that set fire to an oil depot in Sevastopol.
Kyiv's military says undermining Russia's logistics is part of preparations for a long-expected counteroffensive.
Reuters
