Afghan President Hamid Karzai will continue to defy U.S. threats to walk away from a security agreement between the two countries and plans to reiterate in a speech to a grand council later Sunday that he will not sign it before spring, his spokesman said.

"They have waited this long, they can certainly wait five more months," spokesman Aimal Faizi said Saturday of the U.S. The Barack Obama administration has characterized the deal, whose terms Karzai agreed to last week, as a "final offer" that must be completed by the end of the year.

Karzai appears certain Washington is bluffing, saying through the spokesman that he does not believe the United States will resort to the "zero option" of canceling plans to leave a residual troop force to train the Afghan military and continue counterterrorism operations after it withdraws its combat forces from the country in December 2014.