Washington. A preliminary US intelligence assessment concluded that the plane crash presumed to have killed Russian mercenary leader Yevgeny Prigozhin was intentionally caused by an explosion as Russian President Vladimir Putin on Thursday eulogized the man who staged the biggest challenge to his 23-year rule.

One of the US and Western officials who described the initial assessment said it determined that Prigozhin was “very likely” targeted and that the explosion falls in line with Putin’s “long history of trying to silence his critics.”

The officials, who spoke on the condition of anonymity because they were not authorized to comment, did not offer any details on what caused the explosion, which was widely believed to have also killed several of Prigozhin's lieutenants to avenge the mutiny that challenged the Russian leader’s authority.

Pentagon spokesman Gen. Pat Ryder said press reports that a surface-to-air missile took down the plane were inaccurate. He declined to say whether the US suspected a bomb.

Details of the intelligence assessment surfaced as Putin expressed his condolences to the families of those who were reported to be aboard the jet and referred to “serious mistakes" by Prigozhin.

The jet carrying the founder of the Wagner military company and six other passengers crashed Wednesday soon after taking off from Moscow with a crew of three, according to Russia's civil aviation authority. Rescuers found 10 bodies, and Russian media cited anonymous sources in Wagner who said Prigozhin was dead. But there has been no official confirmation.

President Joe Biden, speaking to reporters Wednesday, said he believed Putin was behind the crash, though he acknowledged that he did not have information verifying his belief.

“I don’t know for a fact what happened, but I’m not surprised," Biden said. “There’s not much that happens in Russia that Putin’s not behind."

The passenger manifest also included Prigozhin's second-in-command, who baptized the group with his nom de guerre, as well as Wagner's logistics chief, a fighter wounded by US airstrikes in Syria and at least one possible bodyguard.

It was not clear why several high-ranking members of Wagner, including top leaders who are normally exceedingly careful about their security, were on the same flight. The purpose of their joint trip to St. Petersburg was unknown.

At Wagner’s headquarters in St. Petersburg, lights were turned on in the shape of a large cross, and Prigozhin supporters built a makeshift memorial, piling red and white flowers outside the building Thursday, along with company flags and candles.

In this first comments on the crash, Putin said the passengers had “made a significant contribution” to the fighting in Ukraine.

“We remember this, we know, and we will not forget,” he said in a televised interview with the Russian-installed leader of Ukraine’s partially occupied Donetsk region, Denis Pushilin.

Putin recalled that he had known Prigozhin since the early 1990s and described him as “a man of difficult fate” who had “made serious mistakes in life, and he achieved the results he needed — both for himself and, when I asked him about it, for the common cause, as in these last months. He was a talented man, a talented businessman.”