In a statement, Mr. Manafort’s spokesman, Jason Maloni, suggested that the Party of Regions was accountable for the contradiction between the two disclosures.

“Any questions about the reporting obligations of the Party of Regions should be directed to those within the party responsible for such reporting,” he said in a statement. Mr. Manafort’s work in Ukraine “was widely known and the firm was paid only for the work it performed. In fact, just last month Ukraine officials indicated that there is no proof of illicit payments.”

Though documents discovered after the 2014 revolution show the party’s coffers were padded with donations from Ukraine’s ultrawealthy steel and natural gas tycoons, it tried to keep up a populist image and declared only a modest, even minuscule, annual budget.

“It means either Manafort is lying, or the Party of Regions was lying,” Serhiy Leshchenko, an investigative journalist and a member of Parliament who has been critical of Mr. Manafort’s work in Ukraine, said in an interview.

A Ukrainian investigation of this discrepancy is not likely. The Party of Regions is now disbanded, and prosecutors are looking into far more serious crimes than campaign finance filing errors.

Moreover, at the time the party made its declarations, filing a false campaign finance report was considered an administrative offense akin to a parking ticket and punishable by no more than a fine of a few hundred dollars, said Ostap Kuchma, a party finance analyst at the anticorruption group Chesno.

Mr. Manafort’s reports to the Justice Department do not cover the entire period he worked in Ukraine. Last summer, The New York Times reported that the party’s handwritten ledgers showed $12.7 million in undisclosed payments designated for Mr. Manafort’s firm from 2007 to 2012.