The U.S. has said the potential for sanctions on Russia's oil and gas flows is "certainly on the table. ": It may only be a matter of time before the U.S. and Western allies impose full sanctions on Russia's energy exports, analysts say, warning that such a move would have seismic repercussions for oil and gas markets and the world economy. It comes as Russia's onslaught on key Ukrainian cities enters its second week, with fighting raging in the north, east and south of the country.