MOSCOW — Russia's Federal Security Service (FSB) said on Sunday that a minor had been detained over a threat to carry out a terrorist attack in a Moscow park following a tip-off from the United States, the Interfax news agency reported. The arrest came after the US Embassy in Moscow issued a security alert on Saturday, warning it was “aware of a credible threat of a mass casualty event” at the Tsaritsyno Museum Reserve in Moscow. On Saturday, the FSB said it had received information from the US through established partner channels about preparations for an attack in Moscow and was taking appropriate measures. The agency said it was “grateful to the US side for the information provided.”The Russian teenager had posted photographs of himself on TikTok wearing tactical clothing and a balaclava, holding an object that looked like an automatic weapon, as well as photographs taken at Moscow's Tsaritsyno Museum Reserve with the caption: "I found a place," Interfax cited the FSB as saying. The institution said it was not aware of any warnings. However, several events scheduled to take place at the venue were later canceled and security measures were put in place, according to Russian state media. The FSB said the teenager subscribed to a neo-Nazi channel on Telegram and made a “significant number of search queries regarding past terrorist acts, mass murders, and other violent acts.” It said airsoft weapons were found at the suspect’s home. It is not unusual for the US to share security warnings with other countries — the State Department has a long-standing “duty to warn” policy and is obligated to let US expat communities know of any threats. The alert issued on Saturday said the US government was “coordinating with appropriate Russian authorities on a response.”However, Russia has not always received US warnings with thanks. In March 2024, during the Biden administration era, the US embassy in Moscow warned that ISIS militants were determined to target Russia, specifically saying there were “imminent plans to target large gatherings in Moscow,” including at concerts. Russian President Vladimir Putin dismissed that warning as a provocation. Days later, assailants stormed Moscow’s Crocus City Hall venue and killed more than 140 people. ISIS claimed responsibility for the attack. Putin’s reaction was different in 2017, during US President Donald Trump’s first presidency, when the US warned Moscow about a planned terror attack at the Kazan Cathedral in St Petersburg. According to a Kremlin statement, Putin personally thanked Trump for the information, saying it was enough to locate and detain the suspects. The latest warning and the FSB’s public statement thanking the US, comes at a time of increased scrutiny of the Trump administration’s relationship with Russia. Trump has made significant concessions to Russia on sanctions in recent weeks, which have triggered criticism on both sides of the aisle in Washington and driven a wedge between the US and its Western allies.