An image of Maria Butina pulled from Facebook. (Obtained by The Washington Post)

Maria Butina, who pleaded guilty in December to conspiring with a senior Russian official to infiltrate conservative American political circles as an undeclared Kremlin agent, is continuing to cooperate with investigators and her case is not ready for sentencing, prosecutors said Tuesday.

U.S. prosecutors requested and a federal judge agreed to wait until March 28 to decide the date for a sentencing hearing for Butina, 30. She previously agreed to help U.S. investigators probing her efforts on behalf of the Russian government to forge ties with gun rights advocates at the National Rifle Association and other U.S. conservatives leading up to the 2016 U.S. election.

“We are not prepared to set a sentencing date or to request a sentencing date at this point,” Assistant U.S. Attorney Erik Kenerson said in a brief hearing in federal court in Washington. “We inform the court, in open court, the defendant’s cooperation is ongoing.”

Butina attorney Robert N. Driscoll said the former American University graduate student is ready to learn her punishment, but he added: “We take [prosecutors] at their word. They have other contingent matters that may require cooperation later.”

U.S. District Judge Tanya S. Chutkan accepted prosecutors’ request after a sealed conversation with both sides about what matters were pending that could involve Butina’s help. The judge noted afterward that Butina had good reason to seek sentencing promptly, because she has been in custody since being charged in July.

“Ms. Butina has been detained for a substantial portion of whatever sentence she likely faces,” Chutkan said. “However, given her agreement . . . her cooperation continues to be needed by the government.”

According to her plea deal, Butina began acting on behalf of the Russian government in 2015 and continued her work after moving to the United States to attend graduate school at American University in 2016.

As part of that plea, Butina admitted to working at the direction of Alexander Torshin, a Russian former government official, and with an American political operative to forge connections with officials at the NRA, conservative leaders and 2016 presidential candidates, including Donald Trump.

The political operative has been identified by government officials as Paul Erickson, a longtime GOP political adviser from South Dakota who managed the 1992 presidential campaign of Pat Buchanan.

Erickson, who was also Butina’s boyfriend, was indicted this month in South Dakota over what federal prosecutors said was an unrelated investment-fraud scheme.

Erickson’s attorney, William Hurd, has said his client is a “good American” who “has never done anything to hurt our country and never would.”

Butina is expected to be deported to her native Russia after completing her sentence.