A pundit on Russian state TV has made a stinging attack on new US ambassador Michael McFaul, suggesting he is on a mission to promote revolution.
Mikhail Leontyev noted that Mr McFaul had worked for the National Democratic Institute (NDI), which he said was close to US intelligence services.
Mr McFaul has defended talks he held with opposition figures this week.
Prime Minister Vladimir Putin is standing for re-election as president in March.
Anger over ballot-rigging at parliamentary elections last month developed into the biggest anti-government protests seen in Moscow since Soviet times.
Alexei Navalny, the anti-corruption blogger who initiated the protests, did not attend the ambassador's reception.
However, Mr Leontyev sought to link him to the US ambassador, describing the blogger as the opposition's "internet fuehrer", trained by the NDI.
The accusation that opposition leaders are working at the behest of the US state department to generate an Orange-style revolution is an insult frequently levelled by Kremlin supporters.
Outside Russia, Mr McFaul is regarded as one of America's leading experts on Washington's relations with Moscow, and has been involved in the Obama administration's efforts to "reset" them.
"The thing is that McFaul is not a Russia specialist, but a specialist in a very specific kind of democracy promotion," Mr Leontyev said on Channel One's prime-time news programme on Tuesday evening.
"In Russia, in 1992, he already represented the NDI, known to be close to American special services and engaged in training political leaders for Third World countries.
"In 2010, under a programme by the same institute in Yale, the leader of the next generation of democrats - internet fuehrer Alexei Navalny, a good acquaintance of the same McFaul - was trained."
Mr Navalny attended the 2010 World Fellows programme at Yale, described by the university as a class to train "emerging leaders worldwide". Citizens of EU states, as well as developing countries, are listed among the Fellows.
The ambassador's reception on Tuesday was reported at length by Channel One, under the screen caption "US embassy: Receiving instructions from the new ambassador".
Names of opposition politicians were read out, including Oxana Dmitriyeva, Ilya Ponomaryov, Sergei Mitrokhin, Boris Nemtsov, Vladimir Ryzhkov and Yevgenia Chirikova.
'Friends old and new'
Mr McFaul also paid visits to the Kremlin and Russian government.
In a message on Twitter, Ambassador McFaul commented: "Saw old friends at... Kremlin and new friends at embassy. This is going to be fun."
He added in a message addressed to Mr Navalny: "Yesterday my mtgs with... Kremlin officials could not have been warmer. pluralism!''
On Wednesday, Russian tycoon Mikhail Prokhorov and veteran liberal politician Grigory Yavlinsky each submitted the 2m signatures required to stand in the election on 4 March.
It will be another 10 days before the electoral commission announces whether their applications are valid, and the final line-up for the election is known.
Recent opinion polls suggest Mr Putin would win just under 50% in a free and fair ballot, thus triggering a second round of voting.