In 2016, while Mr. Manafort was chairman of the Trump campaign, anti-corruption prosecutors in Ukraine disclosed that a pro-Russian political party had earmarked payments for Mr. Manafort from an illegal slush fund. Mr. Manafort resigned from the campaign a week later.
The court’s ruling that what the prosecutors did was illegal comes as the Ukrainian government, which is deeply reliant on the United States for financial and military aid, has sought to distance itself from matters related to the special counsel’s investigation of Russia’s interference in the 2016 presidential race.
Some of the investigation by the special counsel, Robert S. Mueller III, has dealt with Mr. Manafort’s decade of work in Ukraine advising the country’s Russia-aligned former president, Viktor F. Yanukovych, his party and the oligarchs behind it.
After President Trump’s victory, some politicians in Ukraine criticized the public release by prosecutors of the slush fund records, saying the move would complicate Ukraine’s relations with the Trump administration.
In Ukraine, investigations into the payments marked for Mr. Manafort were halted for a time and never led to indictments. Mr. Manafort’s conviction in the United States on financial fraud charges related to his work in Ukraine was not based on any known legal assistance from Ukraine.
Two Ukrainian members of Parliament had pressed for investigations into whether the prosecutors’ revelation of the payment records, which were first published in The New York Times, had violated Ukrainian laws that, in some cases, prohibit prosecutors from revealing evidence before a trial.
Both lawmakers asserted that if the release of the slush fund information broke the law, then it should be viewed as an illegal effort to influence the United States presidential election in favor of Hillary Clinton by damaging the Trump campaign.
The Kiev District Administrative Court, in a statement issued Wednesday, said that Artem Sytnik, the head of the National Anti-Corruption Bureau of Ukraine, the agency that had released information about the payments, had violated the law. The court’s statement said this violation "resulted in meddling in the electoral process of the United States in 2016 and damaged the national interests of Ukraine."
A spokeswoman for the anti-corruption bureau said she could not comment before the court released a full text of the ruling. In an interview last June, Mr. Sytnik said he had revealed the information "in accordance with the law in effect at the time."
The court also faulted a member of Ukraine’s Parliament, Serhiy A. Leshchenko, who had commented on Mr. Manafort’s case and publicized at a news conference materials that the anti-corruption bureau had already posted on its website.
Mr. Leshchenko said he would appeal the ruling, and that the court was not independent and was doing the bidding of the Ukrainian government as it sought to curry favor with the Trump administration.
"This decision of the court is for Poroshenko to find a way to Trump’s heart," he said, referring to President Petro O. Poroshenko. "At the next meeting with Trump, he will say, ‘You know, an independent Ukrainian court decided investigators made an inappropriate move.’ He will find the loyalty of the Trump administration."
Mr. Leshchenko said the prosecutors’ revelations about Mr. Manafort were legal because they were "public interest information," even if they were also potential evidence in a criminal investigation.
Mr. Manafort has not been charged with a crime in Ukraine, and earlier this year, Ukrainian officials froze several investigations into Mr. Manafort’s payments at a time when the government was negotiating with the Trump administration to purchase sophisticated anti-tank missiles, called Javelins.
Ukraine’s prosecutor general said the delay on Mr. Manafort’s cases was unrelated to the missile negotiations. In total, the United States provides about $600 million in bilateral aid to Ukraine annually.
Earlier this month, the special counsel accused Mr. Manafort of violating a cooperation agreement by lying. Two of the five alleged lies, according to the filing, related to meetings or conversations with Konstantin V. Kilimnik, Mr. Manafort’s former office manager in Kiev, whom the special counsel’s office has identified as tied to Russian intelligence and as a key figure in the investigation into possible coordination between the Trump campaign and Russia.
Ukrainian law enforcement officials last year allowed Mr. Kilimnik to leave for Russia, putting him out of reach for questioning.
By Andrew E. Kramer, The New York Times