In an interview published Sunday by the Washington Post, Karzai also said that the United States had been supportive of Kabul's positive relationship with Iran, despite the enmity between Washington and Tehran. Asked about the strength of the Taliban in their attacks inside Afghanistan, Karzai suggested that the group has external backers.
"They would not be strong without support," he said. Karzai, who had just returned from Pakistan, declined to specify who is backing the Taliban, which US intelligence has said receives support from tribal areas on Pakistan's western border.
But Karzai said that "Pakistan and Afghanistan and the United States and the rest of the world must join hands in sincerity in order to end this problem." He said that he found Pakistan President Pervez Musharraf "more cognisant of the problems of extremism and terrorism."
"And that's a good sign, and I hope we will continue in that direction."
"We have to end extremism. We have to end support to extremism in the region," he added.
"Unless we do that, the picture is one of doom and gloom - for Pakistan, and as a consequence for Afghanistan." Karzai applauded the US support for his government in Afghanistan- including the planned deployment of 3,2000 US Marines - and the battle against terrorism as "fundamental and strong."
But he added: "It will make a difference when the Americans are clear and straightforward about this fight," saying the US should "mean what they say .. (and) do what they say."
He said that Washington had encouraged Kabul in its close relationship with Iran, despite US-Iran tensions. "We have had a particularly good relationship with Iran the past six years. It's a relationship that I hope will continue," Karzai said.
"The United States very wisely understood that it was our neighbour and encouraged that relationship," he said. "We don't like a nuclear region, of course. Nobody wants nuclear weapons ... But the United States has been very understanding and supportive that Afghanistan should have a relationship with Iran."