Obama administration officials took that as confirmation of their suspicion that the conversation was intercepted or at least disseminated by Russia’s government, which has sheltered Edward J. Snowden, the National Security Agency contractor who exposed American eavesdropping of foreign leaders like Angela Merkel of Germany.

While the revelation prompted the White House to cancel surveillance of friendly foreign leaders like Ms. Merkel, administration officials defended themselves by noting that many governments spy on American officials as well. American diplomats have long assumed that their telephone calls were tapped by Moscow, but rarely if ever have the Russians made recordings public.

The administration official, who spoke on the condition of anonymity, said the fact that this one was made public was a sign of desperation by the Russians, who in this view are trying to stop the Americans from brokering a settlement of the standoff between President Viktor F. Yanukovych and the Ukrainian opposition. It came to light even as Ms. Nuland was in Kiev on Thursday talking with both Mr. Yanukovych and opposition leaders.

Mr. Loskutov, responding to messages from a reporter on Twitter, rejected the American assertion that he was first to disseminate the recording. “Disseminating started earlier,” he wrote in English, adding that his Twitter post was being “used to hang the blame” on Russia. Asked if Russia had any role, he said: “How would I know? I was just monitoring ‘the Internets’ while my boss was off to a meeting with the Chinese leader.”

In the recorded call, Ms. Nuland and the ambassador, Geoffrey Pyatt, were talking about an offer made on Jan. 25 by Mr. Yanukovych to bring two opposition leaders, Arseniy P. Yatsenyuk and Vitali Klitschko, into the government as prime minister and deputy prime minister, respectively. The two Americans described Mr. Yatsenyuk, a former economics minister, in favorable terms, but viewed Mr. Klitschko, a former world heavyweight boxing champion now serving in Parliament, more warily.

“The Klitschko piece is obviously the complicated electron here,” Mr. Pyatt said.

Ms. Nuland suggested that Mr. Klitschko should not go into the government. “I don’t think it’s necessary,” she said. “I don’t think it’s a good idea.”

Mr. Pyatt concurred. “In terms of him not going into the government, just let him sort of stay out and do his political homework and stuff,” the ambassador said. “I’m just thinking in terms of sort of the process moving ahead; we want to keep the moderate democrats together.”