The Taliban on Saturday warned of a prolonged war in Afghanistan if any foreign troops stay after the end of 2014, as Kabul and Washington prepare to discuss the "residual" US security presence.

US President Barack Obama and Afghan President Hamid Karzai will hold talks in the US next week on a long-term security pact between the two countries, with US troops remaining in Afghanistan at the top of the agenda.

"If America wants to leave a small or large number of its troops for whatever length of time then it means war and destruction will continue in the region for that same length," the Taliban said in a statement.

The US Defense Department has prepared plans for a smaller presence in Afghanistan after the White House insisted on examining the option of leaving fewer troops in the country after 2014 than was initially proposed, The Wall Street Journal reported late Friday.

The newspaper said the plans now prepared by the Pentagon call for leaving roughly 3,000, 6,000 or 9,000 US troops in the country.

Those troops would launch strikes against militants and continue training the Afghan army and police, who will be responsible for national security more than a decade after a US-led alliance ousted the Taliban regime in 2001.

US Defense Secretary Leon Panetta has said the slimmed-down force would focus on preventing Al Qaeda, which was sheltered by the 1996-2001 Taliban government, from regaining a foothold in the war-shattered nation.

General John Allen, commander of US and NATO forces in Afghanistan, had earlier suggested leaving 6,000 to 15,000 US troops, the Journal pointed out.

The US and its allies are currently negotiating commitments to Afghanistan on the basis of a formula that calls for US troops to make up two-thirds of any follow-on force, The Journal said.

AFP