KABUL: Afghanistan's future security will remain dependent on international troops for many years after most foreign combat forces leave by the end of 2014, the US commander of the Nato-led force in the South Asian country said.

With the formal security handover to Afghans closing in, intense debate is underway about how many troops the United States and its mainly Nato allies should leave behind to conduct training, support and counter-terror operations.

The White House favours about 7,000 US troops, but some in the US military would prefer two or three times as many.

However many there are left behind, they will play a vital role in supporting the Afghan National Security Forces. ANSF numbers have been projected at 352,000 by the time they take over, although they have not reached that level yet, according to some official US estimates.

US General Joseph Dunford, the last commander of the Nato-led mission in Afghanistan, would not be drawn on how many he thought should remain, referring instead to “sustainability”.

In an interview with Reuters on Tuesday he argued for a significant presence after the US-dominated International Security Assistance Force (Isaf) is disbanded next year.

“The post-2014 presence is a lot more complicated than the numbers and the numbers have become a distraction, to be honest with you,” Dunford said in his Kabul headquarters.

“It's about a lot more than numbers. It's about what capability is required to sustain the Afghan security forces after 2014,” he said.

Twelve years into the war, launched in the aftermath of the Sept 11 attacks on the United States, the Taliban and other insurgents are still able to make telling blows against foreign troops and Afghan government institutions.

That makes the decision about the post-2014 force, to be made in Washington later this year, even more important. Others, such as Germany and Italy, will make smaller contributions.

Isaf currently numbers about 87,000 troops, three-quarters of them American. Dunford said the intense debate about the size of the residual force was not helpful.

One of the sticking points about that force has been the suspension of talks between Afghanistan and the United States over a bilateral security pact to replace the Isaf mission.

The collapse of a similar pact between the United States and Baghdad in 2011 led Washington to pull all its troops out of Iraq, which has since descended back into sectarian violence.

The pact talks were suspended in June amid Afghan anger over the opening of a Taliban office in Qatar, which President Hamid Karzai's government blamed partly on U.S. involvement.

Dunford said he had talked “at every level from district and province to members of parliament ... to President Karzai” and was adamant the pact would be signed.

He also said it was too early to judge whether the mission in Afghanistan had been successful, or how America's longest war would be remembered.

“Our objective is a stable, secure and unified Afghanistan.

And we're still working towards that end,” Dunford said.

“And if we achieve the objective ... I think it will be remembered as being successful.”