The White House says U.S. President Joe Biden will give a speech on April 14 on the U.S. withdrawal from Afghanistan.
The announcement, made to reporters by White House press secretary Jen Psaki, came after The Washington Post and Reuters quoted unnamed sources as saying that Biden will withdraw all U.S. troops from Afghanistan by the 20th anniversary of the September 11, 2001, attacks.
The decision will bring an end to the United States' longest war.
Secretary of State Antony Blinken and Defense Secretary Lloyd Austin are expected to brief the decision to NATO allies in Brussels on April 14.
In 2001, U.S.-led forces invaded Afghanistan and toppled the Taliban regime for harboring Al-Qaeda, which was behind the September 11 terrorist attacks in the United States that killed nearly 3,000 people.
The move will keep thousands of U.S. forces in Afghanistan beyond a May 1 troop withdrawal deadline that the administration of former U.S. President Donald Trump negotiated with the Taliban last year.
There are at least 2,500 U.S. troops in Afghanistan. They are supported by about 7,000 NATO troops.
In recent weeks, Biden has warned that the withdrawal deadline will be difficult to meet due to logistical challenges.
The Taliban has threatened to resume hostilities against foreign troops in Afghanistan if they do not withdraw by May 1.
It is unclear if the Taliban will act on their threats after Biden announces his plan for a phased pullout by September.
Biden's decision comes as Turkey announced that it will host a 10-day international peace conference on Afghanistan from April 24 to May 4.
The Istanbul conference, initiated by the United States, is meant to give new impetus to intra-Afghan peace talks that have failed to make progress since they began in September.
Washington is hoping to hammer out a peace deal between the Afghan government and the Taliban aimed at ending decades of war in Afghanistan.
"The overriding objective of the Istanbul Conference on the Afghanistan Peace Process is to accelerate and complement the ongoing intra-Afghan negotiations in Doha on the achievement of a just and durable political settlement," Turkey's Foreign Ministry said in a statement.
The conference is expected to bring together the Afghan government, the Taliban, and a host of regional powers, including Pakistan, Iran, India, China, and Russia.
It is unclear if the Taliban will participate in the conference.
The day before, the militant group said it would not participate if the summit was held on April 16, as was widely expected.
Mohammad Naeem, spokesman for the Taliban's political office in Qatar, told RFE/RL on April 12 that the militant group had yet to decide if it will attend the summit at a later date.