The United States is pressing for Karzai to sign the deal to extend a military presence past 2014, when NATO and United Nations mandates expire and all foreign troops leave the country.
The U.S. says the deal will keep forces in Afghanistan to train and mentor the Afghan army and police, while a smaller presence will go after the remnants of al-Qaida.
A national assembly of Afghan dignitaries approved the deal and demanded that Karzai sign it by the end of next month—which is also America's deadline before it starts planning a full withdrawal at the end of 2014.
Karzai has so far refused.
Afkham also confirmed reports that Karzai will visit Tehran next week.
He last visited Tehran in August to attend the inauguration of President Hassan Rouhani. Kabul has not officially confirmed the trip.
