The cable, attributed to Assistant Secretary of State Daniel Fried, said the diplomat doubted "rogue security elements" could have operated in London, where the Russian dissident Alexander Litvinenko died from radiation poisoning "without Putin's knowledge," The Daily Telegraph reported Thursday.
Putin told CNN "political purposes" may be behind the leaks but they posed "no catastrophe."
However, Putin did appear upset by U.S. diplomats referring to him as "Batman" to Russian President Dmitry Medvedev's "Robin," the BBC reported.
"To be honest with you, we didn't suspect that this would be done with such arrogance, with such a push and, you know, being so unethically done," Putin said.
The communiques are among the more than 250,000 sensitive diplomatic cables WikiLeaks, a whistle-blowing Web site, offered for publication to several newspapers. The documents included communications about U.S. policy in Iran, Pakistan, Korea and other places.
Other State Department cables indicate the United States believed it was "highly unlikely" Russia would extradite Andrey Lugovoy, the prime suspect in Litvinenko's death, because he enjoys "the personal protection of Putin."
A cable from the U.S. consulate in Hamburg, Germany, revealed American suspicions of a cover-up in the death of Litvinenko, who was killed with polonium-210, the Telegraph said.
Other U.S. diplomatic cables describe Russia as a "virtual mafia state," where officials worked with regional leaders and organized crime bosses.
John Beyrle, the U.S. ambassador to Moscow, said in one cable bribery was rampant in the Russian capital.
"The Moscow system is based on officials making money," he wrote. "The government bureaucrats … all accept bribes … ."
Russian media have been selective on WikiLeaks reporting, the BBC said, noting there has been no mention of a mafia state in news bulletins.