Afghan President Hamid Karzai's demand that US special forces leave a flashpoint province came as a surprise to American commanders, who had no advance warning of the order, officials said Monday.

It remained unclear what led Karzai to issue a blunt announcement that US special operations force would have two weeks to withdraw from Wardak, a key province southwest of the capital Kabul, two US officials said.

"We're not aware of any incident that would have generated this kind of response," one official, who spoke on condition of anonymity, told AFP.

In his statement Sunday, Karzai alleged that Afghans working with US forces had tortured and murdered people targeted in Wardak, triggering local outrage.

The Pentagon confirmed that a special panel of Afghan officials and officers from the NATO-led International Security Assistance Fore (ISAF) are looking into Karzai's allegations.

"There has been a joint commission established by ISAF and the government of Afghanistan to look into the issues that surfaced over the weekend," spokesman George Little told reporters.

"We're trying to seek clarity from the government of Afghanistan."

Asked if the United States would withdraw its elite special operations units from the province, Little said: "It's premature to speculate on what the outcome of what our discussions would be."

Secretary of State John Kerry, speaking at a joint press conference with his British counterpart William Hague in London, said he had taken "appropriate note" of the Afghan complaints which would be "evaluated" by ISAF.

Karzai had "had many legitimate evaluations of how sometimes some things have gone or might be changed and be done better. We're working on that.

"I can assure you we are finely tuned to the needs of the Afghan people and to the most effective ways to make this transition together," Kerry added.

Wardak is a deeply troubled flashpoint where a Chinook helicopter was shot down by the Taliban in August 2011, killing eight Afghans and 30 Americans. It was the deadliest single incident for American troops in the entire war.

Karzai has had a troubled relationship with Washington for years and in the past he has often publicly expressed anger after errant US air strikes killed Afghan civilians.

Analysts said Karzai's move conveyed Kabul's growing distrust of NATO and ita desire to impose their authority over local militia, who are trained by US forces but operate independently in the war against the Taliban.