LONDON -- Mourners gathered at a central London mosque Thursday for the funeral of a British doctor who died while in Syrian government custody.

Dr. Abbas Khan, a 32-year-old orthopedic surgeon, died just days before he was apparently due to be released from detention. The circumstances remain in dispute. The Syrian government said he took his own life, but his family in Britain rejects the claim.

The British government has said the Syrian government is responsible.

"My brother, to us, was our star. His star shone on our family," his brother, Shahnawaz Khan, said at the Regent's Park Mosque.

The 32-year-old Khan was detained in Aleppo in November 2012 after he entered Syria to work in a hospital. His family was told of his death 10 days ago.

Prime Minister David Cameron criticized the Syrian regime for its "despicable" treatment of Khan and its refusal to work with the British government to release him.

"Abbas' death is a sickening and appalling tragedy, and it is right that the Syrian regime should answer for it," Cameron wrote to the Khan family in the letter, which was released Sunday.

Khan's family has criticized the British government for not doing more to secure Khan's release.

An inquest is scheduled to begin Friday.

Family lawyer Nabeel Sheikh said after the funeral prayers that the family would decide what if any legal action to pursue once the inquest has been concluded.