ANKARA, Turkey — More than 70 Syrian military officers, including six generals and 22 colonels, have deserted President Bashar al-Assad's army in the past 36 hours and have crossed the border into Turkey, the biggest such defection in months, an official told AFP on Saturday.

The defections of the 71 army officers and two policemen came after Washington said it had proof that Syrian government forces had carried out deadly chemical weapons attacks against rebels and the United States would begin providing military support to the opposition.