Obama warns Afghan leader of complete troop withdrawal

President Barack Obama has warned his Afghan counterpart Hamid Karzai that the U.S. may pull all of its troops out of his country by the year's end. Mr Obama conveyed the message in a phone call to Mr Karzai, who has refused to sign a security agreement. The U.S. insists this agreement must be in place before it commits to leaving some troops behind for counter-insurgent operations and training.
Background:
U.S. planning full Afghan pullout, Obama tells Karzai [BBC]
U.S. planning possible withdrawal of all troops from Afghanistan [CNN]