A St Petersburg court on Monday ordered the detention of two Russian men on terrorism charges who were arrested after a tip-off from US intelligence.
The two are suspected of plotting terrorist attacks in the city during the New Year holidays.
The Dzerzhinsky District Court ruled that the suspects identified as Nikita Semyonov and Georgy Chernyshev should remain in custody pending their trial.
The Federal Security Service (FSB), the main successor to the KGB, said the suspects detained on Friday confessed to plotting the attacks. It said it also seized material proving their guilt.
Russia's state television reported that the suspects had recorded a video swearing their allegiance to ISIS.
The FSB said it was acting on a tip provided by its “American partners.”
On Sunday, Russian President Vladimir Putin called US leader Donald Trump to thank him "for information transmitted through the special services that helped prevent terrorist attacks in Russia", the Kremlin said.
Videos released by the FSB showed its agents rounding up the two suspects and searching their homes.
Mr Putin's spokesman, Dmitry Peskov, said on Monday that the information provided by the US was a "vivid proof of the efficiency" of counter-terrorism co-operation between the countries.
In December 2017, Mr Putin also thanked Mr Trump for a CIA tip-off that helped to thwart bombings in St Petersburg.
The Kremlin said then that CIA information led the FSB to a group of suspects who planned to bomb the Kazan Cathedral and other crowded sites.
