Gates, left, said that Karzai's, right, plans to take control of the country's security were plausible [EPA]

Plans by Hamid Karzai, the Afghan president, to assume responsibility for his country's security by 2014 are a realistic goal and one that Nato should endorse at an upcoming summit in Lisbon, US officials have said.

Robert Gates, the US defence secretary, and Admiral Mike Mullen, chairman of the US Joint Chiefs of Staff, both acknowledged a tough fight ahead but said on Monday during a visit to Australia that they thought Karzai's target was attainable.

"One of the agenda items of the Lisbon summit is to embrace President Karzai's goal of completing the transfer of security responsibility to Afghanistan by 2014," Gates told reporters.

Asked whether he supported its inclusion at the summit and believed it was plausible, Gates said: "Speaking realistically, I would say yes to both questions."

Mullen, who accompanied Gates on his trip, acknowledged that they were "clearly not there" yet.

"But as a target at this point, that makes sense," he said.

The November 19 to 20 Lisbon summit will bring the Afghanistan war into focus following the most violent year in the nine-year-old conflict.

Nato commanders are calling for patience, saying that despite record casualties, real progress is being made in the battle against the Taliban.

Barack Obama, the US president, aims to start bringing US troops home next July, the beginning of a transition in which Afghans are intended to increasingly take the lead in security.

Opponents of Obama's July deadline say it has emboldened the Taliban, sending a signal that the fighters need only to wait until the departure of foreign forces before stepping up activities.

"People say: You picked July 2011 and that lets the Taliban know that there is an end date. Well, I hope the Taliban think that's an end date because it's not," Gates said.

"And they're going to be very surprised come August, September, October and November, when most American forces are still there and still coming after them."

Source: Reuters