Two US service members have been killed by an Afghan soldier in an apparent insider attack in Afghanistan, local police say.
The soldier opened fire on the Americans in Shawalikot district, Kandahar, the office of the province's police chief confirmed to the BBC.
US officials have only confirmed that two soldiers were killed on Monday.
Meanwhile, Secretary of State Mike Pompeo said he would reduce the number of US troops in Afghanistan by 2020.
A news release by Nato stated only that the soldiers had been killed, and that in accordance with department of defence policy, their names would not be released until 24 hours after the soldiers' families had been notified.
It is believed the Afghan soldier was wounded.
Earlier on Monday, Mr Pompeo said President Donald Trump had directed him to decrease the number of US troops in the region by the 2020 presidential election next November.
"He's been unambiguous: End the endless wars," Mr Pompeo said, speaking at the Economic Club of Washington.
"Draw down. Reduce. It won't just be us. We hope that overall the need for combat forces in the region is reduced."
Reuters reported last week that Mr Pompeo and Afghan President Ashraf Ghani had agreed to "accelerate efforts" to end the war with the Taliban, and that Mr Pompeo was "optimistic" about peace negotiations.
There are around 14,000 US troops still in Afghanistan.
The war in Afghanistan is America's longest. It began after US forces led a campaign to overthrow the Taliban in the wake of the 9/11 attacks in 2001.
As the Trump administration looks at exit plans, US negotiators have been involved with peace talks between the Taliban and Afghan officials.
The talks have focused on a safe withdrawal of US troops from the country in return for the insurgents guaranteeing that Afghan territory would not be used by foreign militants, or pose a security threat to the rest of the world.
The Taliban - which once harboured Osama Bin Laden - have said they will not agree to a ceasefire until foreign forces are withdrawn from Afghanistan and have rejected the Afghan government as "a US-imposed puppet regime".
More than 2,400 American troops have lost their lives - at least 10 in hostile conflict so far this year - according to Department of Defence reports.
More civilians were killed last year in Afghanistan than at any time since records have been kept, with 3,804 civilians losing their lives.
Previous attempts at peace have failed in their early stages.
In 2015, talks in Pakistan between Afghan officials and the Taliban broke down after news emerged of the death of the Taliban leader Mullah Omar - with whose authority the Taliban team was supposedly meeting.