"President Vladimir V. Putin of Russia called President Trump on Sunday to thank him for a tip from American intelligence agencies that helped prevent a terrorist attack in Russia..."

"... the Kremlin said in a statement.... [T]he Federal Security Service, the main successor agency to the K.G.B., told Russian media it had detained two suspects preparing an attack on a crowded location in the northern city of St. Petersburg on New Year’s Eve....  Some of the terrorist groups tracked by the United States have also targeted Russia for years, among them the Islamic State. In 2015, the Islamic State claimed responsibility for blowing up a Russian airliner over Egypt, killing all 224 people aboard.... In 2011, the Federal Security Service warned the F.B.I. that an immigrant from Russia living in Boston, Tamerlan Tsarnaev, had associated with Islamist militants. The F.B.I. investigated the tip but closed the case after finding no proof. Two years later, Mr. Tsarnaev and his brother Dzhokhar detonated homemade bombs at the Boston Marathon."

The NYT reports.