(CNN) Serhiy Lyovochkin and Rinat Akhmetov, two Ukrainian oligarchs who had paid Paul Manafort for years for his political work in their country, were the intended recipients of the American polling data that Manafort shared with Konstantin Kilimnik during the 2016 presidential campaign, a person familiar with the matter said on Wednesday.

Special counsel Robert Mueller's team has been circling Lyovochkin and Akhmetov's dealings with Manafort for a while, as they were both key, generous backers of Manafort's Ukrainian lobbying work, prosecutors said at Manafort's financial fraud trial last summer.

The Justice Department initially asked Mueller to look into the pro-Russian Ukrainians' ties to Manafort, a former Trump campaign chairman, because of how they may relate to other allegations of Russian coordination with the Trump campaign.

The sharing of the polling data with Kilimnik was revealed this week , despite being redacted in a court filing, due to a formatting error.

Manafort earned millions from his Ukrainian political work over several years. That included wire transfers from Akhmetov and Lyovochkin through offshore bank accounts, prosecutors said at trial.

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