MOSCOW — After trying a number of methods to silence the dissident Aleksei A. Navalny and his supporters, the Russian authorities tried something new this week: They seized one of his key allies, put him into compulsory military service and sent him to the Arctic.

Ruslan Shaveddinov, 23, a project manager in Mr. Navalny’s Anti-Corruption Foundation, was detained on Monday at his apartment in Moscow. His cellphone’s SIM card was disabled, Mr. Navalny said, so he couldn’t tell his colleagues or lawyer what was happening.

Mr. Navalny’s allies quickly raised the alarm that night, after it appeared that Mr. Shaveddinov had gone missing and they found the door to his apartment smashed in.

The organization’s lawyers and activists — many of them familiar with harassment by the authorities — braced to find Mr. Shaveddinov at a police station, and even filed a missing-person report. But on Tuesday they learned that he was 3,500 miles away, in Novaya Zemlya, a desolate, scantly populated group of islands in the Arctic Ocean, where he will serve at an air defense base.