US troop strength in Afghanistan has reached about 11,000 soldiers, exceeding the previous official level of 8,400 US forces, the Pentagon said.
Lieutenant General Kenneth McKenzie, Pentagon joint staff director, confirmed the higher-than-previously disclosed force strength in a press conference on Wednesday.
The revelation was made in an effort by Defense Secretary James Mattis to promote transparency, Pentagon spokeswoman Dana White said.
President Donald Trump last week announced an expansion of US forces to hike operations against armed groups and to train and advise Afghan government security forces.
The undetermined troop increase is to be added to the existing 11,000.
Washington's involvement in Afghanistan since late 2001 is the longest war in US history.
US raids kill civilians
Afghan provincial authorities earlier on Wednesday blamed 12 civilian deaths on a US air strike, in what would be the second such incident this week of civilian casualties in a bombing raid.
Women and children were among the dead, Logar provincial council member Hasibullah Stanekzai told reporters. The air raid was conducted "by foreign forces" late Tuesday in Bari village near provincial capital Pul-e-Alam, he said.
US forces are the only foreign military conducting air raid in Afghanistan. The strike targeted two well-known Taliban commanders who at the time were hiding in a civilian house, Stanekzai said.
Both Mawlavi Ahmadullah, the Taliban's self-appointed governor for Khoshi district in Logar, and a deputy commander of Taliban forces in the region, Qari Naqibullah, were killed in the raid, along with several other fighters.
A spokesman for the provincial governor, Mohammad Salim Saleh, spoke of "civilian casualties in a foreign forces air strike," but provided no details.
US military spokesman John Ross said: "We are still not clear on what happened there. We are looking into it".
It is the second air raid this week against Taliban forces that also killed civilians.
On Monday, a raid left 13 civilians dead and seven wounded in western Herat province.
The rate of US and Afghan air raids against Taliban and Islamic State of Iraq and the Levant (ISIL, also known as ISIS) has soared recently.
With Afghan forces stretched thin and demoralized, the military is often relying on air strikes as a last resort to drive the fighters back.
According to the United Nations, the number of civilian casualties from US and Afghan air strikes in the first six months of 2017 increased by 43 percent compared to the same period in 2016.