US public support for the Afghan campaign is declining, polls show
US President Barack Obama is to make his long-awaited announcement on US strategy in Afghanistan next Tuesday, the White House has said.
During a visit to the West Point military academy, he will reveal how many extra troops he has decided to send to fight Taliban militants.
An exit strategy is expected to be a key part of the Obama announcement.
White House spokesman Robert Gibbs said on Wednesday that the US would be out of Afghanistan within eight years.
Meanwhile Afghan Taliban leader Mullah Mohammad Omar has again rejected the idea of peace talks with Kabul.
The BBC's Paul Adams, in Washington, says President Obama's address on Tuesday will be one of the key moments of his first year in office.
It is thought the president will commit between 30,000 and 35,000 extra US troops to the campaign - fewer than the 40,000 sought by the US commander in Afghanistan, Gen Stanley McChrystal.
President Karzai urged the Taliban to rejoin the political process
President Obama vowed on Tuesday to "finish the job" in Afghanistan.
On Wednesday, Mr Gibbs said: "We are in year nine of our efforts in Afghanistan. We are not going to be there another eight or nine years."
He added: "Throughout this process, the president has repeatedly pushed and prodded, not simply for how we are going to get a certain number of troops in, but what is the strategy, what has to be implemented ultimately to get them out."
Mr Gibbs said speeding up the training for Afghan security forces was a key element of the exit plan.
The US currently has about 68,000 troops in Afghanistan while its Nato allies have about 42,000.
Nato chiefs are due to discuss sending more troops to Afghanistan in early December.
Meanwhile in a statement posted on a website used by the Taliban, Mullah Omar dismissed a call from President Hamid Karzai for negotiations.
"The people of Afghanistan will not agree to a negotiation which prolongs and legitimises the invader's military presence in our beloved country. Afghanistan is our home," the statement quoted Mullah Omar as saying.
President Karzai was inaugurated last week after winning a controversial election tainted by fraud.