KABUL - US leaders have dismissed President Hamid Karzai's inflammatory comments about the US and the Taliban engaging in "daily" talks without involving the Afghan leadership.

The US envoy to Afghanistan told TOLOnews Monday that any suggestion Americans were working with the Taliban to remain in Afghanistan after 2014 was "inconceivable".

"The thought that we would collude with the Taliban flies in the face of everything we have done here and is absolutely without foundation. It is inconceivable that we would spend the lives of America's sons, daughters, and our treasure, in helping Afghans to secure and rebuild their country, and at the same time be engaged in endangering Afghanistan or its citizens," Ambassador James Cunningham said.

Karzai on Sunday said at a public gathering that "the senior leaders of the Taliban and the Americans are engaged in talks in Europe and the Gulf state every day" and suggested that the US was supporting an environment of fear around the post-2014 years in order to remain in Afghanistan.

The US Secretary of Defence Chuck Hagel downplayed Karzai's statement after meeting with the president himself.

"It wouldn't make a lot of sense, it seems to me, but, again, I spoke clearly and directly, as the president did, on this issue. And I think he understands where we are and where we've been and hopefully where we're going together," Hagel told reporters in Kabul.

Hagel met with Karzai in private after the joint press conference scheduled for Sunday was cancelled by the US over security concerns.

"We did discuss those comments. I told the president it was not true that the United States was unilaterally working with the Taliban and trying to negotiate anything. The fact is, any prospect for peace or political settlements - that has to be led by the Afghans," he said of the meeting.

"He [Karzai] has his ways," Hagel added. "There will be new challenges, there will be new issues. It shouldn't come as a surprise... but I don't think any of these are challenges that we can't work (our) way through."

Top US and ISAF commander in Afghanistan Gen Joseph Dunford also rejected Karzai's comments over the Taliban-US relationship as "categorically false".

"We have no reason to be colluding with the Taliban, we have no reason to be supporting instability in Afghanistan," Dunford told reporters Sunday.

"We've fought too hard over the 12 years, we have shed too much blood over the past 12 years, we have done too much to help the Afghan security forces grow over the last 12 years to ever think that violence and instability would be to our advantage."

Hagel also met with his Afghan counterpart Minister Bismillah Khan at the headquarters of International Security Assistance Force (ISAF) in Kabul.

It was Hagel's first visit abroad in his new role as Pentagon chief. He landed Friday and has conducted meetings with US and NATO troops at Bagram, Jalalabad and Kabul to make his own assessment of America's longest war as it enters its final stretch.

The Taliban has denied that any negotiations with the US have happened since last year's suspension, and said no progress had been made.

The Taliban officially ended talks with the US a year ago amid disagreement about the release of Taliban prisoners from US military prison based in Cuba's Guantanamo Bay. (Tolo News)