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

Russia on Friday vehemently denied having any involvement in the mysterious plane crash that is believed to have killed Wagner Group leader Yevgeny Prigozhin.

"There has been a lot of speculation around this crash [and] the tragic deaths of the plane's passengers, among them Yevgeny Prigozhin. Of course, the West presents all this speculation from a particular angle. All of that is sheer lies," Kremlin spokesperson Dmitry Peskov told reporters while answering questions during a press briefing. "One should rely on facts. For now, there are not many facts, they have yet to be established in the ongoing investigative procedures."

Prigozhin, 62, was a former close ally of Russian President Vladimir Putin. His private paramilitary organization played a key role in Putin's invasion of neighboring Ukraine before briefly launching an insurrection against the Russian military in June. Forces loyal to Prigozhin marched toward Moscow before turning back after several days.

A private jet was en route from Moscow to St. Petersburg on Wednesday when it went down near the village of Kuzhenkino in Russia's Tver region, north of Moscow. All 10 people on board were killed. Prigozhin and Wagner Group co-founder Dmitry Utkin were among the passengers identified on a flight list, according to Russian officials.

The U.S. Department of Defense said Thursday that Prigozhin was "likely" killed in the plane crash.

Travel restrictions remained in place on Sunday on the major M-4 highway near Moscow, according to Russia’s state-run media.

"According to the previously issued regional decisions, traffic restrictions remain in force on the M-4 Don highway near the Moscow Region and the Tula Region," the federal road agency said, according to TASS.

The security checkpoints had been put in place Saturday as a column of Wagner Group forces traveled toward Moscow. Roadblocks in southern Russia, including in Rostov-on-Don and the Krasnodar Region, were reportedly lifted.

"All previously imposed restrictions on highways have been lifted," TASS reported, citing a branch of the Russian Interior Ministry.

-ABC News' KJ Edelman