Russia's security services said Friday that they had arrested three people from "a Central Asian country" who were plotting an attack in the south of the country, news agencies reported.The FSB said in a statement that it had "put an end to the terrorist activities of three nationals from a Central Asian country who were planning to commit a terrorist act by blowing up a device in a public place in the Stavropol region," the agencies said.Russian television showed images of several men pinned to the ground by FSB agents.The RIA Novosti news agency said the ingredients for an improvised explosive device (IED) and chemical substances had been found at the home of one of the suspects.The announcement came a week after last Friday's massacre at the Crocus City concert hall on the outskirts of Moscow, which claimed at least 144 lives.The Stavropol region sits in the North Caucasus region of southern Russia, bordering Dagestan and Chechnya among other regions.