The stunning reversal came a few weeks before the case — a spinoff of special counsel Robert S. Mueller III’s probe — was set to go to trial.

Assistants to U.S. Attorney Timothy Shea of Washington and Assistant Attorney General for National Security John C. Demers cited an unspecified “change in the balance of the government’s proof due to a classification determination,” according to a nine-page filing accompanied by facts under seal.

Prosecutors also cited the failure of the company, Concord Management and Consulting, to comply with trial subpoenas and the submission of a “misleading, at best” affidavit by Yevgeniy Prigozhin, a co-defendant and the company’s founder. Prigozhin is a catering magnate and military contractor known as “Putin’s chef” because of his ties to Russian President Vladi­mir Putin.