The Kremlin on Wednesday acknowledged for the first time that a plane carrying Yevgeny Prigozhin, mercenary chief of the paramilitary Wagner Group, was possibly downed on purpose.

Kremlin spokesman Dmitry Peskov told reporters that investigators are looking into the possibility that the 62-year-old Prigozhin was assassinated.

"It is obvious that different versions are being considered, including the version -- you know what we are talking about -- let's say, a deliberate atrocity," Peskov said when asked about the investigation.

The plane carrying Prigozhin and nine others crashed in Russia's Tver region on Aug. 23, killing everyone aboard, according to the press service of Russia's Federal Air Transport Agency.

The crash came about a month after Prigozhin led a chaotic armed rebellion that threatened the longstanding leadership of Russian President Vladimir Putin.

On Friday, Peskov denied speculation that the Kremlin was involved in the plane crash, calling the allegation an "absolute lie."

The crash investigation is being conducted by the Russian Investigative Committee as a domestic incident and Peskov said that allowing in international investigators "is out of the question."

-ABC News' Will Gretsky

Ukraine conducted a massive drone attack in Crimea Thursday night into Friday morning, Ukraine Defense Intelligence spokesman Andrii Yusov told ABC News.

An attack was made on the Russian 126th Separate Guards Coastal Defense Brigade of the Black Sea Fleet in the village of Perevalne, Yusov said.

"We are still calculating enemy losses at the moment," Yusov said

-ABC News' Ellie Kaufman

The explosion that downed a plane carrying Wagner Group leader Yevgeny Prigozhin and nine others in Russia was likely caused by a bomb, two U.S. officials told ABC News on Friday.

A senior U.S. official said the preliminary belief is that the private jet was downed Wednesday by an explosion on board, potentially caused by a well-placed bomb.

Another U.S official said the United States believes that a bomb was very likely the cause of the explosion.

-ABC News' Josh Margolin and Luis Martinez

Russian President Vladimir Putin had no recent meetings with Yevgeny Prigozhin, Kremlin spokesman Dmitry Peskov said Friday.

We don't know yet how long the investigation procedures will be," Peskov said when asked if Putin will attend Prigozhin's funeral.

"The president has a busy schedule in general," he added.

Peskov would not comment on the cause of the plane crash.

-ABC News' Anastasia Bagaeva and Ellie Kaufman

U.S. President Joe Biden will make a "memorable speech" before world leaders in Lithuania's capital on the final day of a high-stakes NATO summit, according to National Security Council Senior Director for Europe Amanda Sloat.

Biden's remarks on Wednesday afternoon will focus on similar themes to what he said during his speech in Poland in late February marking one year since Russia waged war on Ukraine.

"President Biden will talk about the strength of the NATO Alliance and how it remains a force for global security and stability, as it has for more than seven decades. He'll talk about how NATO is more vital to our shared future and that didn't happen by accident," Sloat told reporters during a press briefing in Vilnius on Wednesday morning.

"As the president has talked about before, Vladimir Putin thought he could break our resolve when he invaded Ukraine. But our NATO allies and our partners around the world responded by coming together to support the brave people of Ukraine as they defend their freedom, their independence and their democracy," she added.

Beyond addressing the strength of the NATO alliance and the importance of standing by Ukraine, Biden will also look to pitch cooperation like we've seen for Ukraine to tackle other major challenges facing the world, "including the climate crisis, emerging technologies, upholding the international rules of the road and expanding opportunities so we build an economy where no one gets left behind," according to Sloat.

-ABC News' Molly Nagle