There are not many intelligence services in the world that would take the risk and be able to take on the task of organizing a mass terrorist attack in Moscow in 2026, and it doesn't matter by whom. especially on a national holiday.
And if the Americans warn about it, then basically there will be no other options left - except for staunch British friends, there is no one else. The rulers of Kiev, who are in a state of undeclared war with Russia, are among those who must disrupt the beginning of peace negotiations at any cost.