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WASHINGTON — Federal investigators working for Special Counsel Robert Mueller are keenly focused on President Donald Trump's role in crafting a response to a published article about a meeting between Russians and his son Donald Jr., three sources familiar with the matter told NBC News.

The sources told NBC News that prosecutors want to know what Trump knew about the meeting and whether he sought to conceal its purpose.

The meeting occurred at Trump Tower in June 2016 and was attended by Donald Trump Jr., Trump campaign chairman Paul Manafort, and Trump's son-in-law Jared Kushner. The meeting, which was first reported by The New York Times, also involved Russian attorney Natalia Veselnitskaya and former Soviet intelligence officer Rinat Akhmetshin.

Related: Trump 'Weighed In' on Son's Misleading Statement About Russia Meeting

At the time, the White House confirmed that Trump had "weighed in" as the response to the Times report was drafted aboard Air Force One on July 8 as the president returned to the U.S. from the G20 meeting in Germany. The Washington Post reported that Trump had "dictated" the response.

The initial response by Donald Trump Jr. that was drafted aboard Air Force One described the 2016 meeting as "a short introductory meeting. I asked Jared and Paul to stop by. We primarily discussed a program about the adoption of Russian children that was active and popular with American families years ago and was since ended by the Russian government, but it was not a campaign issue at the time and there was no follow up."

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According to The Times, he added: "I was asked to attend the meeting by an acquaintance, but was not told the name of the person I would be meeting with beforehand."

By the next day the paper reported that the meeting was scheduled in order to convey damaging information about Hillary Clinton and her campaign — an account that Trump Jr. would confirm in a follow-up statement and in emails that he released publicly.

Related: Former Soviet Counterintelligence Officer at Trump Tower Meeting With Trump Jr.

In a June 3, 2016, email, publicist Rob Goldstone told Trump Jr. that a Russian prosecutor had "offered to provide the Trump campaign with some official documents and information that would incriminate Hillary [Clinton] … and would be very useful to your father."

Trump Jr. responded, "[I]f it's what you say, I love it."

Emails show that the following day, Goldstone and Trump Jr. began arranging the Trump Tower meeting.

A person familiar with Mueller's strategy said that whether or not Trump made a "knowingly false statement" is now of interest to prosecutors.

"Even if Trump is not charged with a crime as a result of the statement, it could be useful to Mueller's team to show Trump's conduct to a jury that may be considering other charges."

Ty Cobb, the attorney chosen by the White House as special counsel to oversee its response to the Mueller investigation, told NBC News that he assumed “the statement issued after the G20 is of interest, but I'm not aware of any crime associated with that. It was true at the time it was written and true now."

Cobb said that the statement "was not a bible of events leading up to and after the meeting, but it was not untruthful," pointing to the additional details that Donald Trump Jr. and his attorney have since made public.

"It was a simple response to a short request," said Cobb, and the president's role in crafting the statement was "minimal.”

Julia Ainsley and Hallie Jackson reported from Washington, and Tom Winter from New York.