British Prime Minister David Cameron has written to the family of a British doctor who died in a Syrian jail, saying Damascus must "answer for" his "sickening" death.

A government source said on Sunday that the prime minister wrote to the family of Abbas Khan: "Abbas' death is a sickening and appalling tragedy and it is right that the Syrian regime should answer for it."

The body of Abbas Khan, a surgeon from London, has been returned to the UK on Sunday for a post-mortem examination.

Khan died just days before he was apparently due to be released from Syrian government detention.

Syrian authorities say the doctor committed suicide, a notion his family rejects.

His family says the Syrian government is responsible for his death.

The 32-year-old was captured in November last year after he entered Syria to work in a hospital.

Source: AFP And AP