A contract killer has been dispatched to assassinate the Russian double agent who betrayed Anna Chapman and nine other spies in the United States this spring, according to reports in Moscow.

"We know who he is and where he is," a high-ranking Kremlin source told the reputable Kommersant newspaper.

"You can have no doubt – a Mercader has already been sent after him."

Ramón Mercader was the KGB-hired Spanish communist who was sent to kill Leon Trotsky with an icepick in Mexico in 1940.

The traitor was reportedly identified as a Colonel Shcherbakov, an officer of the SVR (foreign intelligence service) who headed the S directorate of the service's US department, which controlled the ring of sleeper agents, including Chapman.

Shcherbakov is thought to have fled Russia three days before the president, Dmitry Medvedev, visited Barack Obama on 24 June, when the two leaders ate hamburgers together at a diner in Virginia.

"After that, the Americans, worried that we would suspect a betrayal and start pulling our agents from the US, began to arrest them," said the Kremlin source.

The agents, who had been living apparently innocent suburban lives in New York, Arlington and elsewhere, were detained by the FBI in late June and convicted of conducting long-term "deep-cover" surveillance on behalf of Russia.

The 10 were later sent to Russia in exchange for the release of four men jailed there for alleged espionage on behalf of the CIA and MI6.

Speaking shortly after the agents' return to Moscow, Russia's prime minister, Vladimir Putin, said the traitor who had betrayed them had been identified.

"It was the result of treason," he said, predicting a grim future for those responsible. "It always ends badly for traitors: as a rule, their end comes from drink or drugs, lying in the gutter. And for what?"

The apparent admission that a killer has been sent after Shcherbakov is surprising. In the post-Soviet period, Moscow has consistently claimed that the last time it ordered a hit was when operatives killed Stepan Bandera, the Ukrainian nationalist, in 1959.

However, two murders in London have raised suspicions that assassinations abroad were never cancelled.

Georgi Markov, a Bulgarian dissident, died in 1978 near Waterloo Bridge after a poison pellet was fired into his leg from the tip of an umbrella.

And in 2006, the former KGB agent Alexander Litvinenko died after allegedly being poisoned with radioactive polonium.

The Kremlin source hinted at a similar end for Shcherbakov: "The fate of such a person is unenviable. All his life he will drag this with him, living every day in fear of retribution."