Washington( CNN) Donald Trump's 2016 campaign chairwoman Paul Manafort continued to keep in touch with his Russian associate Konstantin Kilimnik and discuss Ukrainian politics while he was working for the campaign and through last year, and that's become a central issue of Robert Mueller's special counseling investigation, according to a transcript of a closed-door court hearing.

Mueller prosecutor Andrew Weissmann told a federal magistrate Monday that a session Manafort and Kilimnik had in August 2016 was “of significance to the special counsel.” A redacted version of the transcript was released Thursday.

At the meeting, Ukrainian policy — and, it appears according to previous filings, a peace scheme that would have benefited Russia — came up. Manafort in interviews with the special attorney said the discussion with Kilimnik about the topic objective then.