Since 2013 the White Helmets have saved thousands of lives in Syria, rescuing people from bombings and missile strikes.
The Foreign Secretary said:
I am appalled by the targeted and heinous murders of heroic White Helmets volunteers who put their own safety at risk to save lives on all sides of the Syrian conflict.
Their bravery and humanity is so inspiring and their deaths a huge loss for their families, Syria and the world.
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