Wagner Group leader Yevgeniy Prigozhin was “likely” killed in a plane crash Wednesday, according to an initial U.S. assessment, Brig. Gen. Patrick S. Ryder, the Pentagon spokesman, told reporters at a news conference, writes The Washington Post.

U.S. intelligence officials are considering the possibility that the plane crashed after an explosion aboard, according to U.S. officials familiar with the preliminary assessment.

There is no indication thus far that the jet was downed by a missile, according to three U.S. officials, who like others spoke on the condition of anonymity to discuss a preliminary assessment. An explosion was detected along the path of the plane, but there are no signs of a missile launch, two officials said.

In Russian President Vladimir Putin’s first remarks on the plane crash in the Tver region, he appeared to eulogize Prigozhin, but stopped short of confirming his death. He promised a full investigation, saying it would take “some time”. He said he had known Prigozhin since the 1990s, calling him a “talented person” who “made serious mistakes”.

The Embraer business jet, which listed the mercenary group chief among its passengers, crashed northwest of Moscow, killing all 10 on board, according to Russia’s civil aviation agency.