KYIV, Ukraine (AP) — 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. Ukraine denied any involvement, saying Moscow could use it for further escalation of the war.

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 am.

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.

Ukraine presidential adviser Mykhailo Podolyak denied any involvement.

“Ukraine has nothing to do with drone attacks on the Kremlin,” he said. He 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 US 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 US 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.