Giving evidence to the parliamentary International Development Committee, he broke down as he described children's accounts of being shot by quadcopters.
Labour MP Sarah Champion, who chairs the committee, said his evidence was "profound and deeply chilling".
The 62-year-old surgeon told MPs: "What I found particularly disturbing was that a bomb would drop, maybe on a crowded, tented area and then the drones would come down."
His face shook with emotion as he paused for several seconds to compose himself.
He continued: "The drones would come down and pick off civilians - children.
"We [were] operating on children who would say: 'I was lying on the ground after a bomb had dropped and this quadcopter came down and hovered over me and shot me.'
"That's clearly a deliberate act and it was a persistent act - persistent targeting of civilians day after day."