UK doctor's death in Syria 'in effect murder', says minister
He said it appeared the 32-year-old orthopaedic surgeon from Streatham, south London, had been "murdered by the Syrian regime" in detention.
Dr Khan was arrested last year when he arrived in Aleppo to help civilians.
Mr Robertson said the government was seeking "urgent clarification" about what happened to him.
Dr Khan's family had been told he would be released on Friday, but his brother Afroze said on Monday when his mother went to see her son in Damascus she was told he was dead.
A Syrian government official told the BBC Dr Khan had committed suicide in his cell.
The official said the decision to release Dr Khan this week had involved "the highest authority".
Mr Robertson said: "We can't at the moment be absolutely certain about the circumstances in which Dr Khan met his death, but what is clear is that he went to Syria on a humanitarian mission, was imprisoned by the Syrian authorities and met his death while he was in prison in circumstances that are at best extremely suspicious.
"There is no excuse whatsoever for the treatment that he has suffered by the Syrian authorities who have in effect murdered a British national who was in their country to help people who were injured during their civil war."
BBC
