U.S. says Russia is creating possible "pretext for invasion" of Ukraine

The United States has information indicating Russia prepositioned a group of operatives to conduct a false-flag operation in eastern Ukraine – groundwork for a possible "pretext for invasion," according to a U.S. official.

The official told CBS News on Friday the Russian operatives were "trained in urban warfare and in using explosives to carry out acts of sabotage against Russia's own proxy-forces," and could take action "several weeks before a military invasion, which could begin between mid-January and mid-February."  

The National Security Council declined to specify where the Russian teams were thought to be located.