British authorities said today they thwarted a terrorist plot to blow up aircrafts heading to the US. As a result, officials raised security to its highest level in Britain and banned carry-on luggage on all trans-Atlantic flights. Huge crowds formed at security barriers at London's Heathrow airport (left) as security barred nearly every form of liquid. Heathrow was closed to most flights from Europe, and British Airways canceled all its flights between the airport and points in Britain, Europe, and Libya.