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Two former associates of President Trump — Paul Manafort and Roger Stone — have turned over documents to the Senate Intelligence Committee in its Russia investigation, a congressional source with direct knowledge told NBC News.

Earlier this month, the committee sent document requests to Manafort and Stone, as well as Carter Page and Mike Flynn, officials said previously. The requests sought information pertaining to dealings with Russia. Page has not yet complied, the congressional source said, and Flynn plans to assert his Fifth Amendment right against self-incrimination as a reason not to comply with a committee subpoena, a source close to him has said.

Manafort on the campaign trail in April, 2016. Chip Somodevilla / Getty Images file

The committee’s letter to Page asked him to list any Russian official or business executive he met with between June 16, 2015 and Jan. 20, 2017. It also asked him to provide information about Russia-related real estate transactions during that period. And it seeks all his email or other communications during that period with Russians, or with the Trump campaign about Russia or Russians.

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Similar letters were sent to Manafort and Stone, and those men sent information to Senate investigators by last Friday’s deadline, the congressional source said.

"I gave them all documents that were consistent with their specific request," Stone said in an email to NBC News.

Related: Manafort, Flynn Are Key Figures in Probe Mueller Will Lead

A spokesman for Manafort, Jason Maloni, confirmed that Manafort turned over documents, adding that Manafort remains interested in cooperating with the Senate investigation.

The congressional source said it was too early to tell whether the documents from Manafort and Stone suggested they had fully complied with the request. The source added that the

NBC News has reported that as part of the FBI’s Russia collusion investigation, federal grand juries have issued subpoenas for records relating to both Flynn and Manafort.

Related: Feds Subpoena Records for Mystery Mortgage on Manafort's $3.5M Home

Flynn’s assertion of the Fifth Amendment will make it difficult for the Senate to enforce its subpoena, Senate aides told NBC News. The Senate could go to court, or go ask the Justice Department to go to court to enforce it, but either actin would require the Republicans who control the chamber to agree.

Meanwhile, Flynn can make an argument that his right against self-incrimination extends even to the production of documents that could hurt him, Senate aides said.