In an interview with The Associated Press in Kabul on Sunday, Karzai suggested the hard-line militant leader Mullah Omar should "get in touch" with his government if he wanted to talk peace.
"We reject the offer of talks by Karzai," Mohammed Hanif, who claims to speak for the Taliban, said in a call to an AP reporter in neighboring Pakistan. "Karzai is nothing but a mouthpiece of Americans. Such offers are nothing but a move to weaken our morale."
"It is our policy not to hold talks if foreign occupation troops are in Afghanistan," Hanif added.
Hanif's claim could not be independently verified and his exact ties to the Taliban leadership are unclear.
Karzai's remarks Sunday were seen as a significant softening of the government's previous policy of not negotiating with top leaders of the hard-line militia.
Despite a spike in bloodshed in the country recently, the U.S.-backed leader said the Taliban's resistance was fading although he expected suicide attacks to continue in Afghanistan "for a long time."
Omar has been in hiding since U.S.-led forces ousted his fundamentalist Islamic regime four years ago for hosting Usama bin Laden in the wake of the Sept. 11 attacks.
The Taliban leader has a $10 million U.S. bounty on his head and is believed to be leading holdouts in a rebellion that left about 1,600 people dead last year, the most since 2001.
Karzai, 48, who won a five-year term as the war-battered nation's first democratically elected leader in 2004, invited all Afghans, "Taliban or non-Taliban," to help rebuild the country, and said that includes Omar.
"If he wants to come, he should get in touch with us," the president said, indicating he was open to the possibility of talks with the reclusive militia leader despite his most-wanted status.
Hanif referred to Omar in his comments, saying he was "not in hiding but leading the Taliban movement."