Russia's claims that U.S. plotted drone attack at Kremlin quickly denied

Russia said on Thursday that the United States was behind what it says was a drone attack on the Kremlin that aimed to kill President Vladimir Putin, while Moscow's forces fired more combat drones at Ukrainian cities including the capital Kyiv.

Putin's spokesperson Dmitry Peskov, without providing evidence, said Ukraine had acted on U.S. orders with the alleged drone attack on the Kremlin citadel in the early hours of Wednesday.

Kyiv has denied involvement in that incident, which followed a string of explosions over the past week targeting freight trains and oil depots in western Russia and Russian-controlled Crimea. Moscow has blamed Ukraine for those attacks too.

"Attempts to disown this [attack on the Kremlin], both in Kyiv and in Washington, are, of course, absolutely ridiculous. We know very well that decisions about such actions, about such terrorist attacks, are made not in Kyiv but in Washington," Peskov told reporters.

The Kremlin has said it reserves the right to retaliate. Peskov said on Thursday an urgent investigation was under way and that any response would be carefully considered and balanced.

Separately, Russia's foreign ministry said the alleged drone attack "must not go unanswered" and that it showed Kyiv had no desire to end the 15-month old war at the negotiating table.

White House national security spokesman John Kirby quickly rebutted Peskov's claims.

"I can assure you that there was no involvement by the United States in this. Whatever it was did not involve us," Kirby told MSNBC in an interview. "We had nothing to do with this."

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The United States does not encourage or enable Ukraine to strike outside its borders, he added.

Kirby said it was still unclear what exactly happed at the Kremlin.

"We still don't really know what happened" and Washington is still assessing the situation, Kirby said.

Earlier, Russia fired two dozen combat drones at Ukraine, hitting Kyiv for the third time in four days and also striking a university campus in the Black Sea city of Odesa, ahead of a major counteroffensive by Ukraine to recapture occupied land.

There were no reports of any casualties.