Two members of the US-led coalition in Syria - including one British soldier - have been killed, officials said.
'Operation Inherent Resolve' is the international coalition targeting Islamic State in Iraq and Syria.
In a statement, officials confirmed two coalition personnel were killed and five injured by an improvised explosive device last night.
The statement said: "Wounded personnel received immediate care and are being evacuated for further medical treatment.
"The names of the deceased will be released at the discretion of the pertinent national authorities. Details pertaining to the incident are being withheld pending further investigation."
US media reported one of the troops killed was from the US.
While there was no official confirmation of where the blast happened, CBS News quoted a Syrian official as saying a roadside bomb had exploded in the Arab-Kurdish town of Manbij, near the border with Turkey.
The UK's ministry of defence confirmed one British soldier was among those killed.
A spokesperson said: "It is with regret that we must confirm that a member of the UK Armed Forces was killed by an improvised explosive device in Syria yesterday.
"The individual was embedded with US forces on a counter-Daesh operation when the incident occurred. The family has been notified and our thoughts are with them at this difficult time. We cannot confirm any further details at this stage."
The US-led coalition was formally established in 2014, and has conducted thousands of airstrikes in Iraq and Syria alongside limited ground operations.
Officials say at least 800 civilians have been unintentionally killed in strikes against IS, but the Airwars monitoring group puts the death toll at more than 6,000 civilians.