Russia's security service says it has prevented major terrorist attacks after finding a truck packed with a ton of explosives, and a cache of poison.
A federal forces spokesman says authorities detained two men after stopping the truck near Grozny.
The Interfax news agency quotes him as saying the vehicle was fully prepared for an explosion. All one needed was a suicide attacker to switch on a detonator.
The Federal Security Service also reports discovery of a cache of a cyanide-based substance in the North Caucasus that officials say was to be used for a chemical attack.
Security in Russia is extremely tight ahead of the arrival of world leaders for ceremonies Monday marking the 60th anniversary of the end of World War II in Europe.
Monday is also the first anniversary of the assassination of Kremlin-backed Chechen President Akhmad Kadyrov in Grozny.
Some information for this report provided by AP and Reuters.