An RAF drone strike disrupted a public killing being staged by Islamic State in Syria last week, according to the Ministry of Defence.
A sentry from Isis was killed by a Hellfire missile fired from a Reaper drone, the MoD said.
The MoD issues regular updates of airstrikes against Isis targets in Syria and Iraq but this incident stands out from the routine list of snipers, trucks and other targets, not least in offering up details.
An RAF crew monitoring events on the ground at Abu Kamal, in eastern Syria, homed in on a large crowd gathering in one of the town’s main streets on Tuesday 9 May.
A statement by the MoD, which refers to Isis as Daesh, said: “When a van then unloaded two shackled prisoners in front of the crowd, it became clear that Daesh were organising a public execution. Given the large number of civilians present, the Reaper’s crew could not target directly the Daesh fighters about to carry out the murders.
“However, two armed extremists were stationed as sentries on the roof of a building overlooking the scene. A Hellfire missile was fired immediately, and scored a direct hit which not only killed one of the sentries but also brought the execution to an immediate halt, as the Daesh fighters fled the scene, and the crowd of civilians dispersed.”