The US Embassy in Russia issued a warning about a "credible threat" in Moscow's Tsaritsyno Park.
The statement said that the department was made aware of a "credible threat of an event that could result in a large number of victims today" on the grounds of the Tsaritsyno Museum Reserve.
The embassy advised US citizens not to visit the reserve, to monitor the situation around them, to have a charged phone and documents with them.
Before attack in Karchum, the US issued a similar warning.