By David Shepardson and Jeff Mason WASHINGTON (Reuters) -Crews worked to pull the remains of the U.S.' deadliest air disaster in two decades from Washington's Potomac River on Friday, searching for the cause of an incident that has raised questions about air safety and a shortage of tower controllers.

Investigators plan to push forward on Friday with efforts to retrieve the two aircraft involved in a crash in Washington that killed 67 people and raised questions about air safety in the U.S. capital.

WASHINGTON: A US commercial airliner with 64 people aboard and a military helicopter collided over Washington on Wednesday before crashing into the Potomac River, triggering a massive rescue operation that has pulled multiple bodies from the near-freezing water.