Paul Manafort, who was forced out as President Trump’s campaign chairman last summer after five months of infighting and criticism about his business dealings with pro-Russian interests, disclosed Tuesday that his consulting firm had received more than $17 million over two years from a Ukrainian political party with links to the Kremlin.

The filing serves as a retroactive admission that Mr. Manafort performed work in the United States on behalf of a foreign power — Ukraine’s Party of Regions — without disclosing it at the time, as required by law. The Party of Regions is the political base of former President Viktor F. Yanukovych, who fled to Russia during a popular uprising in 2014.

The disclosure hints at the vast fortunes available to top American political consultants plying their trade in other countries.

It was not immediately clear if Mr. Manafort would be required to pay any fines for the late filing. He has maintained that a majority of his work for Mr. Yanukovych was political consulting in Ukraine, where his firm, Davis Manafort International, operated an office at the time.