BOSTON (Reuters) -A Russian-born scientist and research associate at Harvard University who has been held for months in an immigration detention center in Louisiana has been criminally charged with attempting to smuggle frog embryo samples into the United States.

Federal prosecutors in Boston announced the smuggling charge against Kseniia Petrova, 31, hours after a federal judge in Vermont heard arguments in a lawsuit she filed alleging that the Trump administration has been unlawfully detaining her.

She was transferred out of the custody of U.S. Immigration and Customs Enforcement on Wednesday to a nearby Louisiana parish jail after being charged. An initial hearing in her criminal case is set for Thursday.

Petrova's lawyer, Gregory Romanovsky, called the case "meritless" and questioned the timing of her being transferred into criminal custody, saying it happened after the judge in her lawsuit set a May 28 bail hearing to consider releasing her.

"The charge, filed three months after the alleged customs violation, is clearly intended to make Kseniia look like a criminal to justify their efforts to deport her," he said in a statement.

Petrova's detention in February coincided with efforts by Republican President Donald Trump's administration to ramp up deportations and revoke student visas as part its wide-ranging efforts to fulfill his hardline immigration agenda.

Prior to the criminal case being unsealed, the government had indicated it planned to deport her back to Russia, despite Petrova stating she feared going back to country or origin after protesting Russia's war in Ukraine.

She was detained at Logan International Airport in Boston on February 16 after a trip to Paris. Petrova, who worked at Harvard Medical School, has said her boss asked her to bring back frog embryo samples for ongoing experiments.

Federal prosecutors said that upon her arrival, Petrova was stopped by U.S. Customs and Border Protection agents after her checked duffle bag was flagged for inspection, revealing biological material.

Such biological products must be declared and require a permit to be brought into the country. Prosecutors said that Petrova initially denied carrying any biological material in her baggage before admitting she had biological specimens.

Her visa was then canceled and she was taken into custody by immigration officials.

"The rule of law does not have a carve-out for educated individuals with pedigree," U.S. Attorney Leah Foley, the top federal prosecutor in Massachusetts, said in a video posted on X.

(Reporting by Nate Raymond; Editing by Leslie Adler and Sandra Maler)