Barack Obama, the US president, is to announce his administration's plans for the scope and speed of an initial troop withdrawal from Afghanistan.
Obama will outline details in a televised address at 8pm EST on Wednesday [0100 GMT on Thursday].
The president has reportedly been considering several options, all of which deal specifically with the 30,000 "surge" troops dispatched to Afghanistan last year.
One proposal, endorsed by generals at the Pentagon, would remove 5,000 of those troops this summer, with another 5,000 to be withdrawn in six months. The remainder would stay in Afghanistan until late 2012.
A second option would withdraw 15,000 troops this year, while a third would simply set an endpoint, requiring the surge troops to be removed by December 2012 but allowing military commanders to decide the pace of the withdrawal.
Regardless of which plan Obama chooses, all 30,000 "surge" troops will almost certainly be withdrawn by the end of 2012.
More than 68,000 US troops will remain in Afghanistan, likely through 2014.
White House officials have praised the "surge" for improving security in Afghanistan, a theme Obama will likely return to in his Wednesday night address.
"We have more boots on the ground, we have more soldiers engaging," said Jay Carney, the White House press secretary, at a briefing on Tuesday.
"We've been taking the fight to the Taliban, as well as going after members of al-Qaeda. And that has been why we've had the success we’ve had."
US officials say security gains are 'tenuous,' partly because Afghan troops are not ready to take over
Security has indeed improved in parts of Afghanistan, particularly in areas of the south.
Lashkar Gah, the capital of Helmand province, is largely under the control of the Afghan government; it is one of seven areas where Afghan forces are scheduled to take over security next month.
The list includes three full provinces - Bamiyan, Panjshir and Kabul, all of them among the most secure in Afghanistan - and four cities.
In neighbouring Kandahar province, meanwhile, residents say the Taliban has lost its grip over many rural areas.
But those gains are not uniform: Lashkar Gah has seen an influx of refugees escaping violence elsewhere in Helmand; and in Kandahar, the Taliban have shifted focus to the provincial capital, where they have launched several high-profile attacks this month.
Northern Afghanistan, meanwhile, has seen an increase in violence over the last two years.
Admiral Mike Mullen, the chairman of the US joint chiefs of staff, said last year that he was "concerned" about the rising violence.
Mullen also called the security gains "tenuous," a widely-shared view in the military.
Robert Gates, the outgoing US defence secretary, has said repeatedly that any withdrawal from Afghanistan should be gradual.
Falling support for war
A larger withdrawal would be unpopular at the Pentagon, but it would be unlikely to meet much resistance from a US public increasingly tired of the war.
A Washington Post-ABC News poll released last month found that 64 per cent of Americans believe the war in Afghanistan is "no longer worth fighting."
An even larger group, 73 per cent, support a "substantial withdrawal" of US troops next month.
The AP news agency released its own poll earlier this month, which found that 80 per cent of Americans support the plan to begin withdrawing troops this summer.
Support for the war is also slipping on Capitol Hill: A bipartisan group of 27 senators sent a letter to Obama last week arguing that the mission in Afghanistan has largely been completed.
"There are those who argue that rather than reduce our forces, we should maintain a significant number of troops in order to support a lengthy counterinsurgency and nation-building effort," the senators wrote. "This is misguided."
In the House of Representatives, meanwhile, the appropriations committee approved a new outside review panel to examine US policy in Afghanistan and Pakistan.
A major concern for politicians is the cost of the war - $6.7bn per month, according to Pentagon figures from February, the most recent month for which data is available.
A senate report released earlier this month found that billions of dollars of US development aid in Afghanistan have been poorly spent on short-term projects.
'Hurtful and inappropriate'
Obama's announcement comes at a time of heightened diplomatic tension between Washington and Kabul.
Hamid Karzai, the Afghan president, delivered a blistering address on local television on Saturday in which he accused the US of "poisoning" the environment in Afghanistan, and of causing damage to roads and other infrastructure.
"You remember a few years ago I was saying thank you to the foreigners for their help, every minute we were thanking them," Karzai said.
"Now I have stopped saying that, except when Spanta forced me to say thank you," referring to his national security adviser, Rangin Spanta.
Karl Eikenberry, the US ambassador in Kabul, called Karzai's remarks "hurtful and inappropriate".