>>>higher. tonight, the u.s. state department issued a warning any american planning to travel to the olympics in russia , this is about the potential danger following the terrorist threats and the opening ceremony is exactly four weeks from tonight. our chief foreign correspondent richard engel has more, what brought this about today, richard?
>> reporter:good evening, brian, we understand there is no specific threat, but security is the overwhelming concern that russia has in the lead-up to these games. and russia is imposing some very severe security restrictions, already banning all liquids on flights, not just large amounts of liquids but any liquids of any kind. also about 40,000 police and soldiers are imposing a so-called ring of steel around the venues at sochi. the fsb, which is the new kgb is responsible for security overall. the main concern, obviously, is terrorists, specifically somebody coming from the north caucasuses. and earlier there were bombings that put the officials on alert. the u.s. is not concerned about the olympic venues themselves but concerned something could happen at a train station or a transport hub, a softer target that could be attacked during the game.
>>richard engel in moscow, as we said the opening ceremony four weeks from tonight, thank