In at least two meetings with Mr. Manafort, Mr. Moreno and his aides discussed their desire to rid themselves of Mr. Assange, who has been holed up in the Ecuadorean Embassy in London since 2012, in exchange for concessions like debt relief from the United States, according to three people familiar with the talks, the details of which have not been previously reported.

They said Mr. Manafort suggested he could help negotiate a deal for the handover of Mr. Assange to the United States, which has long investigated Mr. Assange for the disclosure of secret documents and which later filed charges against him that have not yet been made public.

Within a couple of days of Mr. Manafort’s final meeting in Quito, Robert S. Mueller III was appointed as the special counsel to investigate Russian interference in the 2016 election and related matters, and it quickly became clear that Mr. Manafort was a primary target. His talks with Ecuador ended without any deals.