MOSCOW - The "swine" who exposed the 10 Russian sleeper spies in the United States will not be tracked down and killed, Prime Minister Vladimir V. Putin said Thursday, saying Russia had abandoned the Soviet-era practice of killing turncoats.

"Russia's special services don't do that," he said during a televised call-in show. "As for the traitors, they will croak all by themselves. Whatever equivalent of 30 pieces of silver they get, it will get stuck in their throats."

The role played by a Russian intelligence officer in exposing the sleeper spies was first reported last month by the newspaper Kommersant. President Dmitry A. Medvedev confirmed the report, saying only that he had "found out about it on the day it happened."

Addressing the betrayal directly Thursday for the first time, Putin said the spies had been exposed by a fellow intelligence officer.

"Those people sacrificed their lives to serve the Motherland, and there happened to be an animal who betrayed them," Putin said. "How will he live with it all his life? How will he look his children in the eye? Swine!"

After the 10 agents returned to Russia in early July following a spy swap, Putin met with them and led them in singing patriotic songs. Medvedev bestowed the highest state awards on them in a Kremlin ceremony in October.

Putin, a KGB veteran who led the main Russian spy agency before becoming president in 2000, insisted in a recent CNN interview that the agents had caused no damage to the United States.

Russian officials in the past have issued similar denials that the special services were engaged in killing turncoats.

Alexander Litvinenko, a former KGB officer-turned-Kremlin critic who died in London in 2006 after ingesting radioactive polonium, blamed Putin for the poisoning. Russia denied any role in the killing and refused Britain's demand to extradite the main suspect, former KGB officer Andrei Lugovoi.

Russian security services also denied involvement when a former separatist president of Chechnya, Zelimkhan Yandarbiyev, was killed in a bomb explosion in Qatar in 2004. Two Russian intelligence agents were convicted in Qatar and later returned to Russia.