The Kremlin says Russian President Vladimir Putin, in a telephone conversation initiated by the Russian side, has thanked U.S. President Donald Trump "for information transmitted via the special services that helped prevent the commission of terrorist acts in Russia."
There was no immediate confirmation from the U.S. side about the alleged plot.
Russian media later cited the Federal Security Service (FSB) as saying two Russians "who wanted to carry out [a] terror attack in St. Petersburg on New Year's holidays" were detained on the basis of the U.S. tip.
The Putin-Trump call also reportedly included discussion of "a set of issues of mutual interest," according to the official Kremlin website.
Both leaders, Putin's office said, agreed "to continue bilateral cooperation in the fight against terrorism."
No other details were provided.
Relations between Moscow and Washington have been tense amid ongoing sanctions and counter-sanctions over Russia's invasion of Ukraine five years ago, the abandonment or looming expiration of milestone arms-control treaties, and seemingly clashing alliances and priorities in trouble spots like Syria and Venezuela, among other things.
Trump and Putin's relationship has been under intense scrutiny since U.S. intelligence agencies concluded that Russia meddled in the 2016 U.S. elections that vaulted political outsider Trump into the White House.
They have had at least six face-to-face meetings since Trump assumed the presidency in 2017, including in Osaka during a G20 summit in June, when Trump emerged to tell reporters that what the two men said to each other was "none of your business."
TASS noted that Russian officials had credited the United States with sharing information about terrorist plots in October and in 2017.