US President Barack Obama and his Afghan Counterpart Hamid Karzai reaffirmed during a phone call their commitment to the mission in Afghanistan which is critical to the security of both countries and agreed to stay in close contact. President Karzai expressed his condolences over the death of American soldiers in ISAF helicopter crash in east Afghanistan on Saturday, the White House said in a statement. For his part, Obama noted the extraordinary service of the Americans who gave their lives, and expressed his condolences for the Afghans who died serving by their side, according to the statement. On Saturday, a military helicopter crashed in eastern Afghanistan, killing 31 US troops and seven Afghans aboard.