Sixty passengers and four crew members from the plane and three Black Hawk helicopter personnel are feared dead as a recovery mission is underway.

By Trevor Hunnicutt, David Shepardson and Jeff MasonWASHINGTON (Reuters) -Scores of people were feared dead after an American Airlines regional passenger jet carrying 64 people collided with a U.S. Army Black Hawk helicopter and crashed into the frigid Potomac River near Reagan Washington National Airport.

U.S. authorities said on Thursday it was not yet clear why a regional jet crashed into a U.S. Army helicopter at a Washington airport, killing 67 people in the deadliest U.S. air disaster in more than 20 years.