The police said they also retrieved secret NATO documents believed to have been handed over to the Russians in previous meetings with Mr. Biot. The Russian envoys were not identified by name, and the role of the second diplomat was not immediately clear.
Neither Italian nor Russian officials indicated that their response to the episode would escalate.
“We will continue acting in line with our geopolitical position and our values,” Luigi Di Maio, Italy’s foreign minister, told senators on Wednesday. “But also safeguarding our fundamental interests, which require us to maintain a critical but constructive interlocution with Russia and China.”
The Russian Embassy in Rome said in a statement that it considered it “inappropriate” to comment, but said it hoped the case would “not impact on the bilateral relationship” between Russia and Italy.
In Russia, the official reaction was also low key, suggesting the Kremlin had no intention of playing up the incident.
A Russian lawmaker, Leonid Slutsky, who is chairman of Parliament’s international affairs committee, said his country would retaliate, the Interfax news agency reported. But the Kremlin spokesman, Dmitri S. Peskov, told journalists in a conference call that Russia hoped to maintain good relations with Italy despite the incident.
Andrew E. Kramer contributed reporting from Moscow.