Two US servicemen have been shot dead and six others are injured after a machine gun attack in eastern Afghanistan.
American officials in the country said a combined US-Afghan force, stationed in the province of Nangahar, had been targeted by an individual in an Afghan uniform.
Colonel Sonny Leggett, a spokesman for US forces in Afghanistan, said "the cause or motive behind the attack is unknown at this time".Image: Donald Trump wants to pull US troops out of Afghanistan
The violent incident comes at a sensitive time for the US operation in Afghanistan, with American diplomats having struggled to make progress in negotiations with the Taliban that would see foreign troops head home.
In exchange, the Taliban would be expected to provide security guarantees, including a commitment to ensure Afghanistan will not again become a base for international terrorist groups like al Qaeda.
But with violence in the country having failed to ebb away, the 13,000 US troops still stationed in Afghanistan do not seem likely to leave anytime soon.
Back in December, a mid-ranking Taliban commander told Sky News there cannot be a ceasefire - or any talks with the US-backed Afghan government - until all foreign forces leave Afghanistan
The foreign troops are there as part of a US-led NATO mission to train, assist and advice Afghan forces and carry out counter-terror operations in the country.
Nangahar is particularly significant to the latter, as it has long served as the main stronghold of Islamic State and has also been partly controlled by the Taliban.Image: Donald Trump at Bagram airbase
During a surprise Thanksgiving visit to Afghanistan last year, Donald Trump told US troops at Bagram Airfield that he was confident negotiations with the Taliban would eventually succeed.
He said: "The Taliban wants to make a deal. We'll see if they want to make a deal. It's got to be a real deal. But we'll see, but they want to make a deal."