The decision to back Karzai's intention came at a peace conference, or jirga, Friday of government-appointed delegates, who also pressed for the removal of some insurgents from a U.N. sanctions list and the release of some detainees in U.S. custody, The Washington Post reported.
The delegates also called for the U.S.-led international force to take greater steps to avoid civilian casualties.
The Taliban, which sees the Karzai government as one imposed on the country after a foreign invasion, condemned the three-day conference and attacked near the jirga site on the opening day.
Organizers of the conference conceded the difficulty in reaching a truce with the Taliban.
"The struggle for obtaining peace has not ended," said Burhanuddin Rabbani, who is leading the conference.
Some Afghans, including delegates, said no substantive progress would come out of the meeting.
"I was not satisfied," said Muhtara Maha Bibi, 42, a delegate from Badghis province in northeastern Afghanistan. "Everything we concluded was already planned."
Others among the 1,600 delegates pointed to the need for jobs and a decent standard of living.
"Fifty percent of the Taliban are good people," said Mohammed Khabir Amani, 39, a delegate from Takhar province in northeastern Afghanistan. "Something must be done for them in terms of jobs, a place to live and security."