Former national security adviser Michael Flynn provided "substantial assistance" in the special counsel's Russia investigation and should receive little to no prison time, federal prosecutors said in court papers filed Tuesday.

Flynn met with special counsel Robert Mueller's team and Justice Department lawyers 19 times after he pleaded guilty to lying to federal investigators, according to a sentencing memo filed by Mueller's office.

The court papers offered few new details on the Russia probe but the prosecutors, citing Flynn's extensive cooperation in "several ongoing investigations," said a sentence that includes no prison time is "appropriate and warranted."

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"The defendant provided firsthand information about the content and context of interactions between the transition team and Russian government officials," reads the heavily redacted memo.

The memo says Flynn began providing information to investigators "not long after the government first sought his cooperation."

"His early cooperation was particularly valuable because he was one of the few people with long-term and firsthand insight regarding events and issues under investigation by (Mueller's office)," the memo says.

Flynn's cooperation extends to a "criminal investigation" that is separate from Mueller's probe, according to the court documents. But the federal prosecutors released no details on that investigation, redacting nearly the entire section devoted to it.

Rudy Giuliani, President Donald Trump's outside attorney, told NBC News Tuesday night that he's not concerned that Flynn shared anything with the special counsel that could implicate Trump.

"If he had information to share with Mueller that hurt the president, you would know it by now," Giuliani said. "There's a Yiddish word that fits," Giuliani said, in a brief phone interview. "They don't have bupkis."

Giuliani insisted that "maybe this will convince all of America there was no collusion."

The sentencing memo also says that Flynn lied to the Justice Department about his ties to Turkey. He made the false statements in documents that he filed to register as a foreign agent with the Justice Department. In the documents, Flynn disclosed that in August 2016 he began working on a project that benefited Turkey and paid his company $530,000, the memo says.

But Flynn left out that Turkish government officials were in charge of the project, according to the court papers. On election day, he wrote an op-ed article that called for the removal of Fethullah Gülen, an exiled Turkish cleric living in Pennsylvania, but failed to disclose that the column was motivated by his lobbying work on behalf of the Turkish government, the memo says.

Flynn pleaded guilty in December 2017 to a charge of lying to the FBI about his conversations with Russian ambassador Sergey Kislyak in the weeks before President Donald Trump took office.

The crime carries a maximum sentence of five years in prison, but his plea agreement says he's eligible for a sentence of six months or less. Flynn's sentencing is set for Dec. 18.

In his plea, Flynn admitted to discussing U.S. sanctions with Kislyak in a phone call in late December 2016 and said senior members of the incoming Trump administration were aware of his efforts, which undermined the policies of the outgoing Obama administration. Flynn had urged Kislyak not to overreact to sanctions imposed by the Obama White House in response to Russian meddling in the presidential election the month before.

Flynn had earlier made "material false statements and omissions" when confronted by FBI agents about the conversations, according to court papers.

The Flynn-Kislyak phone call created turmoil in the early days of the Trump administration and sparked fresh questions about its ties to Russia.

The White House denied that Flynn had discussed sanctions with Kislyak during the call, and Vice President MIke Pence later said that Flynn had assured him that sanctions never came up.

On Jan. 26, 2017, then-acting Attorney General Sally Yates told White House counsel Don McGahn that sanctions had in fact been discussed in the call and warned that Flynn was susceptible to blackmail by the Russians.

But it wasn't until 18 days later, on Feb. 13, that Flynn was forced to resign. The White House said Flynn, a decorated retired Army lieutenant general, was fired for misleading Pence and other senior officials about his discussions with Kislyak.

Flynn, who was forced out after just three weeks on the job, is so far the only member of the Trump administration to plead guilty to a charge brought by Mueller as part of his probe into Russian election interference and potential ties to the Trump campaign.

As part of the investigation, Mueller's prosecutors have been trying to piece together what happened inside the White House over that 18-day period, according to multiple people familiar with the matter.

Meanwhile, the filing of the Flynn sentencing memorandum came amid a flurry of activity in the Mueller investigation.

Trump's former personal attorney Michael Cohen pleaded guilty last Thursday to lying to Congress about plans for a Trump Tower in Moscow.

Cohen admitted that he was not being truthful when he told the Senate Intelligence Committee that the Moscow project "ended in January 2016 and was not discussed extensively with others" in the Trump Organization.

Court documents filed by Mueller's office said the talks continued into June 2016 — in the heat of the presidential race — and for a time included discussions with Trump, his children and Russian government officials.

On Friday, Mueller's office is expected to file court papers detailing why the special counsel is withdrawing a plea agreement with former Trump campaign chairman Paul Manafort. Prosecutors say Manafort breached his plea deal by lying to federal prosecutors after agreeing to cooperate in the Russia probe.

And on Dec. 12, Cohen is expected to be sentenced in federal court in New York.