WASHINGTON (Reuters) -A leading U.S.-India relations expert and U.S. government adviser arrested over handling of classified documents will vigorously contest the allegations, and specifically any insinuation that he operated on behalf of a foreign adversary, his lawyers said on Wednesday.

Ashley Tellis, 64, who served on the National Security Council of former Republican President George W. Bush and is listed in an FBI court affidavit as an unpaid adviser to the State Department and a Pentagon contractor, was arrested on the weekend and charged on Monday with "unlawful retention of national defense information."

An FBI affidavit accompanying the charge said that in September and October Tellis was observed in Pentagon and State Department buildings accessing and printing classified documents, including about military aircraft capabilities.

The affidavit said a search of Tellis' residence in Vienna, Virginia, on Saturday uncovered more than a thousand pages of classified documents with top secret and secret markings.

The affidavit also said Tellis had met Chinese government officials on multiple occasions, including a September 15 dinner at which it said Tellis arrived with a manila envelope, which he did not appear to have when he left.

"Ashley J. Tellis is a widely respected scholar and senior policy advisor," a statement from his attorneys Deborah Curtis and John Nassikas, with the Arnold & Porter law firm, said.

They said that at a court hearing in the Eastern District of Virginia on Tuesday and in related filings, they would be "vigorously contesting the allegations brought against him, specifically any insinuation of his operating on behalf of a foreign adversary."

Tellis is a senior fellow at Washington's Carnegie Endowment for International Peace think tank. Carnegie said on Wednesday that Tellis is on administrative leave.

Trump administration officials, including Director of National Intelligence Tulsi Gabbard, have vowed to prosecute individuals who mishandle classified information.

The Tellis case has been brought by Lindsey Halligan, U.S. attorney for the Eastern District of Virginia, who was formerly U.S. President Donald Trump's personal lawyer.

Halligan has been leading prosecutions of New York Attorney General Letitia James and former FBI Director James Comey, sparking concern among some former federal prosecutors who say the cases show Trump is using federal power to target political foes.

The Justice Department says Tellis faces up to 10 years in prison and a fine of up to $250,000 if convicted.

(Reporting by David Brunnstrom and Andrew Goudsward; Editing by Don Durfee and Edmund Klamann)