Prosecutors said that Mr. Manafort tried to contact witnesses by phone, through an intermediary and through an encrypted messaging program. One witness told the F.B.I. that Mr. Manafort was trying to “suborn perjury,” prosecutors said. Two witnesses provided the texts to the F.B.I., which also searched Mr. Manafort’s cloud-based Apple account, according to court records…

The witnesses at issue in Monday’s court filing relate to allegations that Mr. Manafort secretly retained a group of former European officials to act as lobbyists on issues related to Ukraine. Mr. Manafort paid them 2 million euros in 2012 and 2013, according to court documents.

Prosecutors say that was part of a secret lobbying campaign in the United States. Mr. Manafort argues the lobbying was focused on the European Union — a key point in his defense.

In court documents, prosecutors accused Mr. Manafort of trying to reach members of a public relations firm who could get word to the Europeans and help shape their story. “They should say their lobbying and public relations work was exclusively in Europe,” one of the public relations officials told the F.B.I. according to court documents.