WASHINGTON — An Iranian judge who sentenced the American graduate student Xiyue Wang to a decade in prison was hit with United States sanctions on Thursday in the Trump administration’s latest pressure offensive against Tehran.

Mr. Wang, a fourth-year graduate student at Princeton University, spent three years in Tehran’s notorious Evin Prison after being convicted of espionage. He was freed this month in a prisoner exchange in which the Justice Department dropped charges against an Iranian scientist, Masoud Soleimani, and allowed him to leave the United States.

The judge in Mr. Wang’s case, Abolghassem Salavati, “is a tool of the regime’s repression — not an impartial friend of justice,” Secretary of State Mike Pompeo said on Thursday.

“We’re glad we won Xiyue’s release, but he should have never been sentenced or jailed in the first place,” Mr. Pompeo said, adding that Mr. Salavati is believed to have sentenced hundreds of political prisoners. “He’s the go-to guy” in the Iranian government’s efforts to detain dissidents, Mr. Pompeo said.