Convicted Russian agent Maria Butina has been released from a Florida prison after serving most of her 18-month sentence for conspiring to influence US conservative activists and infiltrate a powerful gun rights group.

Butina has been taken into custody following her release by immigration officials, to be deported to her native country.

The 31-year-old had been scheduled for release from a low-security prison in Florida in early November, but a change in federal law brought her release date forward for good behaviour, her attorney Robert Driscoll said.

A prison official confirmed she was released on Friday morning and taken into custody by immigration authorities.

Russian President Vladimir Putin has previously expressed outrage over Butina’s prison sentence and said she did not carry out any orders from Russian security services.

Butina, a former graduate student at American University in Washington who publicly advocated for gun rights, pleaded guilty in December to one count of conspiring to act as a foreign agent and agreed to cooperate with prosecutors.

The Siberian native admitted to conspiring with a Russian official and two Americans to infiltrate the National Rifle Association and create unofficial lines of communication to try to shape Washington’s policy toward Moscow.

Her 18-month sentence included nine months she spent incarcerated after her July 2018 arrest.

Butina’s case was separate from former Special Counsel Robert Mueller’s investigation of Russian interference in the 2016 US election, which detailed numerous contacts between Trump’s campaign and Russia.

Her activities occurred during the same period as the contacts investigated by Mueller.

The Russian official with whom Butina conspired was later identified as Alexander Torshin, a deputy governor of Russia’s central bank.

He was never charged in the case, but was hit with sanctions by the US Treasury Department.

-AAP