Russian President Vladimir Putin telephoned US President Donald Trump Sunday to thank him for a CIA tip that helped thwart a series of bombings in St Petersburg, the Kremlin said.

During the call, the two leaders’ second in three days, Putin expressed gratitude for the CIA information. The Kremlin said it allowed Russia’s top domestic security agency to track down a group of suspects that planned to bomb Kazan Cathedral and other crowded sites this weekend.

“The information received from the CIA proved sufficient to find and detain the criminal suspects,” the Kremlin said.

It added that Putin asked Trump to convey gratitude to the CIA and assured him that “if the Russian intelligence agencies receive information about potential terror threats against the United States and its citizens, they will immediately hand it over to their US counterparts via their communications channels".

The CIA’s tip to Russia comes even as Russia-US ties have plunged to their lowest level since the Cold War era — first over Russia’s annexation of Crimea and support for pro-Russia separatists in Ukraine, more recently over allegations that Moscow interfered in the US presidential election to help Trump.

While Russian officials have said the two countries were continuing to exchange a terror-related intelligence, Sunday’s statement from the Kremlin was Russia’s first public assertion that information from the United States helped prevent an attack.

The conversation was the second between the Russian and US presidents since Thursday, when Trump thanked Putin for his remarks “acknowledging America’s strong economic performance”, according to the White House.

During the first call, they also discussed during ways to work together to address North Korea’s nuclear and ballistic weapons programme, the White House said.

The Federal Security Service, or FSB, announced Friday that seven suspected followers of the Islamic State group had been arrested for allegedly planning to carry out terror attacks in St Petersburg this weekend.

The agency said the suspects were plotting a suicide bombing in a church and a series of other explosions in the city’s busiest areas this coming weekend on ISIS orders. It said a search of a St Petersburg apartment found explosives, automatic weapons and extremist literature.

Russian news reports said that Kazan Cathedral, a landmark 19th century Russian Orthodox church on St Petersburg’s central Nevsky Prospect, was the prime target.

If the suspects succeeded in bombing the cathedral, it would have been the first major attack on a Russian Orthodox Church by Islamist terrorists, who have blown up apartment buildings, passenger planes and transport facilities in Russia.

In April, a suicide bombing in the St Petersburg’s subway left 16 dead and wounded more than 50.

Russian TV stations have aired footage daily since Friday of the suspects in the foiled attacks being apprehended and questioned. One segment showed FSB operatives outside a St Petersburg apartment building detaining a suspect, who appeared later saying he was told to prepare homemade bombs rigged with shrapnel.

“My job was to make explosives, put it in bottles and attach pieces of shrapnel,” the suspect, identified by Russian media as 18-year old Yevgeny Yefimov, said in the footage released by the FSB.

Several other suspects came from mostly Muslim regions in Russia’s volatile North Caucasus, and one man was from the ex-Soviet nation of Tajikistan that borders Afghanistan.

The TV reports included footage of a metal container, which the suspects used as a laboratory for making explosives, according to the FSB. Another video showed operatives breaking the doors and raiding an apartment used by other suspects.

Last week, the FSB said it also arrested several ISIS-linked suspects in Moscow, where they allegedly were plotting a series of suicide bombings to coincide with New Year’s celebrations.

The latest calls between Putin and Trump came after the Russian leader praised his U.S. counterpart during a marathon news conference on Thursday.

Putin hailed Trump’s achievements, saying that global markets have demonstrated investors’ confidence in Trump’s economic policies. He said he hoped the US president would be able to follow through on his campaign promises to improve ties with Russia despite pressure from his political foes at home.

During the news conference, Putin also reaffirmed his multiple denials of meddling in the 2016 US presidential election and argued that Washington is only hurting itself with investigations of alleged collusion between Trump and Russia.