Moscow, Russia (CNN) -- Diplomatic cables released by the whistle-blowing website WikiLeaks offer a rare glimpse into the sensitive relationship between the United States and Russia, particularly over past negotiations on Iran's nuclear program.
In one confidential assessment, sent on October 6, 2009, the U.S. ambassador in Moscow, John Beyrle, complains of a "stubborn mentality" among Russian officials, that "instinctively opposes making common cause with the West over Iran."
As the United States worked to build an international consensus over the need for tougher sanctions on Tehran, the cables illustrate growing frustrations in Russia with Iran, as well as a growing sense among Russian policy-makers and analysts that Moscow's influence over Tehran was slipping.
In a cable sent on December 14, 2009, and following backsliding by Iran over an apparent agreement on uranium enrichment, Russian President Dmitry Medvedev is reported to have told Italian Prime Minister Silvio Berlusconi that dealing with Iran was "frustrating" and that he "did not know who was making decisions in Tehran now."
In a separate observation, a senior official at Russia's Foreign Affairs Ministry, Ali Mustafabeily, describes the Iranians as "sly," adding that they knew how to negotiate.
In another candid assessment, Beyrle remarks that Russia's reliance on oil and gas revenues creates what he calls an "instability premium" favoring Russian economic interests. If tension over Iran pushes the price of oil up by $5, Beyrle notes, that equates to an increase of $11-13 billion per year in income for Russia's oil and gas producers.
Dmitry Peskov, a spokesman for Russian Prime Minister Vladimir Putin, told CNN that Russian officials were still going through the released material. "So far, we don't have much of a reaction," he said, adding, "we don't want to be involved in sensationalism."
U.S. diplomats, meanwhile, tell CNN they do not believe there is anything in the released cables likely to cause lasting damage to Washington's relations with Moscow.
CNN's Andrew Carey contributed to this report.