President Barack Obama has authorized an additional 17,000 U.S. troops to be sent to Afghanistan to battle insurgent threats and weak security along the Pakistani border, the White House said Tuesday. “The decision was communicated to the Pentagon yesterday. The orders were signed today,” spokesman Robert Gibbs told reporters traveling with Obama in Denver, Colorado. “This increase is necessary to stabilize a deteriorating situation in Afghanistan, which has not received the strategic attention, direction, and resources it urgently requires,” Obama said in a statement. Obama called sending troops into danger one of a president's most solemn duties. He also said he is withdrawing U.S. soldiers from Iraq, which would give the Pentagon more flexibility in shifting troops to Afghanistan. About 8,000 Marines are expected to be deployed first, followed by about 9,000 Army soldiers. The new forces would be the first installment on a larger increase of U.S. forces widely expected this year.