Russia's Federal Security Service said Sunday that it had detained a minor suspected of plotting an attack at a popular palace and park complex in southern Moscow, and it credited information from American law enforcement with leading officers to him. "We are grateful to the American side for providing the information," the agency said in a statement quoted by the Interfax news agency, according to a Reuters report carried by The Moscow Times.

The detention followed a public warning from Washington. On Saturday, the U.S. Embassy in Moscow issued a security alert saying it was "aware of a credible threat of a mass casualty event" that day at the Tsaritsyno Museum Reserve, urged people to stay away from the area and said the U.S. government was coordinating with Russian authorities on a response, Al Jazeera reported. The FSB said the same day that the United States had passed it information, through what it called established partner channels, about preparations for an attack in the capital, and that it was taking appropriate measures, according to NBC News and Reuters.

The complex was temporarily closed on Saturday and access to the park was restricted, the RIA news agency reported, citing Russian law enforcement. The Russian outlet Baza said an organ concert was halted for the evacuation roughly ten minutes before the end of its program and that a separate concert was later canceled, NBC News reported. When CNN contacted the museum after the alert, the institution said it was not aware of any warnings, but several scheduled events were later called off and security measures were put in place, according to Russian state media cited by CNN.

The account of the suspect comes from the FSB's statement as relayed by the Interfax and TASS news agencies. The agency said the teenager had posted pictures on TikTok showing himself in tactical clothing and a balaclava while holding an object that resembled an automatic weapon, along with photos taken at Tsaritsyno under the caption "I found a place." Officials who searched his home found the clothing and accessories seen in those posts, the FSB said, and his phone showed a subscription to a neo-Nazi channel on Telegram and a large number of searches about terrorist attacks, mass killings and other violence, The Moscow Times reported. The agency also said airsoft weapons were found at the home, CNN reported.

The suspect, a Russian citizen, has not been publicly identified. The FSB said Russia's Investigative Committee is weighing what legal or procedural action to take, Al Jazeera reported.

Sharing threat information with other governments is not unusual for Washington. The State Department has a long-standing "duty to warn" policy that requires it to alert American communities overseas to threats, CNN noted.

Moscow has not always welcomed such warnings. In March 2024, the U.S. Embassy cautioned that extremists had imminent plans to target large gatherings in Moscow, including concerts. President Vladimir Putin dismissed the alert as a provocation, and days later gunmen stormed the Crocus City Hall venue outside the capital and killed more than 140 people in an attack claimed by the Islamic State group, according to CNN and NBC News.

Sunday's public thanks resembled an episode from President Donald Trump's first term. In 2017, after the United States warned Moscow about a planned terror attack at Kazan Cathedral in St. Petersburg, the Kremlin said Putin personally thanked Trump and that the information had been enough to locate and detain the suspects, CNN recalled.

The latest exchange comes despite long-running tensions between Washington and Moscow over Russia's war in Ukraine, Al Jazeera noted.