The brother of Syrian President Bashar al-Assad lost one leg in a July attack on the country's security cabinet in Damascus, a Western diplomat and a Gulf-based source said on Thursday.

"We heard that he (Maher al-Assad) lost one of his legs during the explosion, but don't know anymore," the diplomat told Reuters.

A Gulf source confirmed the report: "He lost one of his legs. The news is true."

The attack on July 18 killed half of the government's six-member crisis council, including the president's brother-in-law Assef Shawkat.

Maher al-Assad has not been seen in public since the attack.

President Assad has been battling a 17-month-old uprising against his rule. The United Nations says at least 18,000 people have died in the revolt.