Cohen is under intensifying scrutiny from federal prosecutors in Manhattan who are examining his business practices, as well as special counsel Robert S. Mueller III, who is continuing to investigate episodes involving Cohen, according to a witness who testified in front of a grand jury in Washington last week.

Andrii V. Artemenko, a former member of the Ukrainian parliament, said in an interview that many of the questions he faced during several hours of testimony Friday were focused on his interactions with Cohen. Artemenko met with Cohen in January 2017 to discuss a back-channel peace initiative for Ukraine.

“I realized that Michael Cohen is a target” of special interest to Mueller, Artemenko told The Washington Post this week, days after he was questioned.