American and other Western officials said an explosion on a plane believed to be carrying the Russian mercenary leader Yevgeny V. Prigozhin likely brought down the aircraft on Wednesday, killing all the passengers aboard, based on preliminary intelligence reports.

A definitive conclusion has not been reached, but an explosion is the leading theory of what caused the plane to crash in a field between Moscow and St. Petersburg. The explosion could have been caused by a bomb or other device planted on the aircraft, though other theories, like adulterated fuel, are also being explored, the officials said.

U.S. officials say American intelligence has not confirmed Mr. Prigozhin’s death, though multiple officials said it appeared likely he was killed in the plane crash. A Western official said that Mr. Prigozhin was on the plane, according to several indicators his country had collected. American satellite intelligence did not detect a missile launch, and there is no other evidence a surface-to-air weapon took out the plane.

The Wagner paramilitary group, which Mr. Prigozhin founded, also did not officially confirm his death.

U.S. and European officials, who spoke on the condition of anonymity to discuss the matter, said they believed President Vladimir V. Putin of Russia ordered the destruction of the plane in an attempt to kill Mr. Prigozhin.

Mr. Prigozhin’s armed rebellion in June against the military leadership was one of the most dramatic challenges to Mr. Putin’s rule in decades. During the brief mutiny, Wagner forces took over a key southern city and an armed convoy of Mr. Prigozhin’s mercenaries marched toward Moscow, making Mr. Putin look weak.

Intelligence and military officials have predicted for weeks that Mr. Putin would retaliate, even as they expressed puzzlement that Mr. Prigozhin appeared to move freely. The mercenary leader showed up at a summit meeting Mr. Putin attended, traveled back and forth from Belarus and recorded a recruitment video.