Foreign policy advisor to US President Donald Trump's election campaign, George Papadopoulos, arrives at US District Court for his sentencing in Washington, DC on September 7, 2018.

George Papadopoulos, a former campaign advisor on Donald Trump's presidential campaign, was sentenced Friday to 14 days in jail for lying to investigators during their probe of Russian interference in the 2016 presidential election.

Papadopoulos, 31, who was also sentenced to one year of supervised release, is the first member of the Trump campaign to be sentenced in special counsel Robert Mueller's ongoing investigation.

"I made a terrible mistake," Papadopoulos said at his sentencing in U.S. District Court in Washington, D.C.

Papadopoulos' lawyers had argued that Trump's constant attacks on Mueller's probe as "fake news" and a "witch hunt" hindered the investigation "more than George Papadopoulos ever could."

Trump's bellicose stance on the probe had influenced Papadopoulos' decision to lie, his lawyer argued.

Defense lawyers had asked Judge Randolph Moss for a sentence of probation. Mueller's prosecutors, however, sought a sentence between zero and six months in prison.

The prosecutors had argued in court filings that Papadopoulos' lies to the government were "material to the investigation" of Russian election interference that preceded the appointment of the special counsel.

Papadopoulos pleaded guilty in October to lying to the FBI about his contacts with London-based professor Joseph Mifsud, who told Papadopoulos in late April 2016 that Russians had "dirt" on Trump's campaign rival, Hillary Clinton.

Trump had weighed in before the sentencing Friday, connecting Papadopoulos' experience with the special counsel to his own tug-of-war over a potential in-person interview with investigators.

"I see Papadopoulos today. I don't know Papadopoulos. I don't know him. I saw him sitting at one picture at a table. That's the only thing I know about him. I don't know him. But they got him on, I guess a couple of lies," Trump said.

Trump was referring to a March 2016 foreign policy in which he shared a table with Papadopoulos and other advisors.

In an interview with The New York Times, Papadopoulos said he informed then-candidate Trump and the other officials during that meeting that Mifsud was interested in scheduling a meeting between Trump and Russian President Vladimir Putin.

"Trump was at least open to this," Papadopoulos said.

"Though he wasn't committed either way, but he nodded and deferred to [Attorney General] Jeff Sessions who I remember being actually quite enthusiastic about a potential meeting between then-candidate Trump and Putin."

The Justice Department did not immediately respond to CNBC's request for comment.