A United States judge on Friday sentenced Russian secret agent Maria Butina to 18 months in prison for conspiring with a Russian official to infiltrate a gun rights group and influence US conservative activists and Republicans.

Key points: Maria Butina admitted to conspiring with a Russian official and two Americans

Maria Butina admitted to conspiring with a Russian official and two Americans Butina has already spent nine months in jail, which will count towards her 18 months sentence

Butina has already spent nine months in jail, which will count towards her 18 months sentence She will be deported to Russia after completing her prison sentence

US District Court Judge Tanya Chutkan imposed a sentence that matched the prison term prosecutors had requested and also agreed to have Butina, 30, deported back to Russia after she completes her incarceration.

The sentence will include the nine months Butina already has already served in jail since her July arrest.

Clad in a green prison jumpsuit, Butina begged the judge for leniency and said she was "deeply sorry".

"For all the international scandal my arrest has caused, I feel ashamed and embarrassed. My parents taught me the virtue of higher education, how to live life lawfully, and how to be good and kind to others," Butina said.

"I have three degrees, but now I'm a convicted felon with [no] job, no money and no freedom," Butina added.

Butina pleaded guilty in December to one count of conspiring to act as a foreign agent and agreed to cooperate with prosecutors.

'No simple misunderstanding'

"This was no simple misunderstanding by an over-eager foreign student," Judge Chutkan said before imposing the sentence.

Butina admitted to conspiring with a Russian official and two Americans from 2015 until her July arrest to infiltrate the National Rifle Association, a group closely aligned with US conservatives and Republican politicians including President Donald Trump, and create unofficial lines of communication to try to make Washington's policy toward Moscow more friendly.

Coincidently, Mr Trump addressed an NRA conference about an hour after Butina was sentenced.

Alexander Torshin, who was a deputy governor of Russia's central bank, has been identified as the Russian official in question.

Mr Torshin was not charged, but he was hit with sanctions by the US Treasury Department in April 2018.

One of the two Americans referenced by prosecutors was Butina's then-boyfriend Paul Erickson, a conservative political activist who has not been charged in this case, but faces criminal charges of wire fraud and money laundering in a separate case in South Dakota.

Prosecutors said that while Butina did not engage in "traditional" spy craft, she worked behind-the-scenes in conservative political circles to establish ties and boost the US-Russia relationship.

That included actions such as arranging dinners in Washington and New York and attending events to meet high-profile politicians.

US pro-gun advocate Maria Butina has been sentenced to 18 months in prison. ( Facebook )

Butina 'bragged about her political connections'

Many of those meetings have been documented on Butina's social media pages, which feature photos of her attending NRA conferences, a high-profile annual prayer breakfast in Washington, and posing for pictures with people including Republican former Wisconsin Governor Scott Walker, a 2016 presidential candidate.

Her lawyers said these activities were not conducted with any malfeasance, and downplayed the crime as a simple failure to notify the Justice Department of her activities on Russia's behalf.

"If I had known to register as a foreign agent, I would have done so without delay," Butina said on Friday. "I just didn't register because I didn't know to."

Prosecutor Erik Kenerson, in his remarks in court, said her activities were more serious than that.

"This is not a registration offense. This is a case where the defendant acted in the United States as an agent of the Russian government," Mr Kenerson said.

The case against Butina was separate from Special Counsel Robert Mueller's 22-month investigation of Russian interference in the 2016 US election, which detailed a series of contacts between Mr Trump's campaign and Russian officials.

Butina publicly supported Mr Trump and who bragged at parties in Washington that she could use her political connections to help get people jobs in his administration.

Reuters