Kyiv | Russia claimed it foiled an attack by Ukrainian drones on the Kremlin early Wednesday, calling it an unsuccessful assassination attempt against President Vladimir Putin and promising retaliation for what it termed a “terrorist” act.

The Ukrainian president denied it, saying “We don't attack Putin or Moscow.” Putin wasn't in the Kremlin at the time and was at his Novo-Ogaryovo residence outside Moscow, his spokesman Dmitry Peskov told Russia's state news agency RIA Novosti.

There was no independent verification of the reported attack on the Kremlin, which Russia authorities said occurred overnight but presented no evidence to support it. Questions also arose as to why it took the Kremlin hours to report the incident and why videos of it also surfaced that late in the day.

A video posted overnight on a local Moscow news Telegram channel, shot from across the river from the Kremlin, appeared to show smoke rising over the buildings. It wasn't possible to ascertain its veracity. According to text accompanying the footage, residents of a nearby apartment building reported hearing bangs and seeing smoke around 2:30 a.m.

The Kremlin said Russian military and security forces stopped the drones before they could strike. Nobody was hurt, it added.

The Kremlin's website said debris from the drones fell on the grounds of the Moscow landmark without damage.

Zelenskyy, on an unannounced visit to Helsinki for talks with the leaders of five Nordic countries, denied any role in the attack.

“We don't attack Putin or Moscow. We fight on our territory. We're defending our villages and cities,” he said at a news conference.

Ukraine presidential adviser Mykhailo Podolyak said the claims would provide a pretext for Russia “to justify massive strikes on Ukrainian cities, on the civilian population, on infrastructure facilities” in coming days.

The Pentagon is looking into the alleged attacks, according to a U.S. official, speaking on condition of anonymity to discuss sensitive matters.

American intelligence officials also were were looking into the Russian claims but had not yet made a determination, according to a U.S. official familiar with the matter. The official spoke on the condition of anonymity to discuss the ongoing assessment.

US Secretary of State Antony Blinken, speaking in Washington at a World Press Freedom Day event, said he had seen the reports but “I can't in any way validate them. We simply don't know.” He added: "I would take anything coming out of the Kremlin with a very large shaker of salt. So let's see. We'll see what the facts are and it's really hard to comment or speculate on this without really knowing what the facts are.” The purported drone attack would be a significant escalation in the 14-month conflict, with Ukraine taking the war to the heart of Russian power.

Phillips O'Brien, professor of strategic studies at the University of St. Andrews, said, “It certainly wasn't an attempt to assassinate Putin, because he doesn't sleep in the roof and he probably never sleeps in the Kremlin.” He added it was too soon to prove or disprove whether it was a Russian attempt “either to make Ukraine look reckless or to buck up Russian public opinion” or if it was a Ukrainian operation to embarrass Russia.

The alleged attack immediately prompted calls in Russia from pro-Kremlin figures in Russia to carry out assassinations on senior leadership in Ukraine.

The Kremlin claimed the attack was planned to disrupt Victory Day, which Russia celebrates in Red Square on May 9 to commemorate the defeat of Nazi Germany in World War II. Peskov said the parade would take place as scheduled.

Shortly before the news about the alleged attack broke, Moscow Mayor Sergei Sobyanin issued a ban on using drones in the Russian capital, with an exception for drones launched by authorities.

Sobyanin didn't offer any reason for the ban, saying only that it would prevent the “illegal use of drones that can hinder the work of law enforcement.” Zelenskyy was in Finland to secure greater firepower for his armed forces as they figure out how to dislodge Russian troops from occupied areas of Ukraine.

Zelenskyy told a Helsinki news conference before Russia's drone attack claims that Ukraine's counteroffensive is coming “very soon.” This year “will be decisive … for victory,” he said.

The Nordic countries — Finland, Sweden, Norway, Denmark and Iceland — have been among Kyiv's strongest backers since Russia's full-scale invasion of Ukraine in February 2022. Before the meeting with Zelenskyy in Finland's capital, Nordic officials appeared ready to provide more aid as the war stretches into its 15th month.

“There is still an urgent need for military support to ensure that the Ukrainians stand as strong as possible in the fight against Russia,” Danish Prime Minister Frederiksen said in a statement.

Norwegian Prime Minister Jonas Gahr Støre, another of the summit attendees, said: “Here in the north, we have a more unpredictable and aggressive Russian neighbor, and it is important that we discuss together how to face this new situation.” The talks came a day after U.S. officials said Washington plans to send Ukraine about $300 million in additional military aid, including an enormous number of artillery rounds, howitzers, air-to-ground rockets and ammunition.

The weapons will all be pulled from Pentagon stocks, so they can go quickly to the front lines, according to the officials who spoke on condition of anonymity because the aid has not yet been formally announced.

Elsewhere, Russia used Iranian-made drones during its third attack on Ukraine's capital city in six days.

Explosions were heard in Kyiv and elsewhere during the night as Ukrainian air defenses shot down 21 of the Russian drones, Ukraine's Air Force Command said. No damage or casualties were reported Meanwhile, a massive blaze broke out at an Russian oil depot, local officials said Wednesday.

The depot erupted in flames in Russia's southern Krasnodar region, located east of the Russian-held Crimean Peninsula, according to Krasnodar Gov. Veniamin Kondratyev.

He didn't say what caused the fire, which was described as extremely difficult to put out. But some Russian media outlets said it was likely caused by a Ukrainian drone attack overnight. There was no official comment on that possibility.

Local residents heard an explosion shortly before the fire erupted, Russian news site Baza said.

Military analysts think Ukraine is targeting supply lines in the Russian rear while gearing up for a possible counteroffensive amid improving weather conditions and as it receives large amounts of weapons and ammunition from its Western allies.

Explosions also derailed a Russian freight train and hit a Russian airfield in recent days. Last weekend, a massive fire erupted at an oil depot in Crimea after it was hit by two of Ukraine's drones, a Russia-appointed official said.

In anticipation of a Ukrainian counteroffensive, Russian forces are focused on destroying logistical routes and centers of Ukraine's armed forces with long-range strikes, Kyiv military officials say.

At the same time, Russia plans to continue talks with the United Nations and other parties to an wartime agreement on facilitating Black Sea agricultural shipments, Kremlin press secretary Dmitry Peskov said ahead of talks on Friday.

Earlier Wednesday, Russian Foreign Ministry spokeswoman Maria Zakharova confirmed a new round of consultations between Russia and the U.N. on access of Russian agricultural products and fertilizers to the world market would be held in Moscow.

Signed in July and renewed twice, most recently in March, the deal unblocked Ukrainian grain shipments that were held up in the country's blockaded ports last year. The deal will expire May 18 unless Russia agrees to its renewal.

In the latest Ukrainian civilian casualties, three people died and five were wounded when what was described as the only working supermarket in the southern Ukrainian city of Kherson came under fire about 11 a.m. Wednesday, according to Ukraine's Ministry of Internal Affairs.

A round-the-clock curfew is to be introduced in Kherson from 8 p.m. Friday through 6 a.m. Monday, Kherson Gov. Oleksandr Prokudin announced.

“During these 58 hours, it is forbidden to move around or stay on the streets of the city. Also, the city will be closed for entry and exit," he said.

The measure is necessary, he said in a video on social media, “so that law enforcement officers can do their job and not put you in danger,” but didn't provide further details.

Both Russia and Ukraine reportedly have experienced ammunition shortages after a winter of long-range shelling and missile strikes. Ukraine's government has been pressing its allies to give it more as officials consider when and how they might start trying to drive Russian forces out of the Ukrainian territory they have occupied.