The leader of an al-Qaeda-linked group that conducted attacks across the Middle East before shifting its focus to Syria's civil war has died in custody in Lebanon.

The detainee, Saudi citizan Majid al-Majid, is reported to have died after suffering kidney failure. He was detained in Lebanon late last month and had been held at a secret location. He was said to be the commander of the Abdullah Azzam Brigades and one of the 85 most-wanted individuals in his native Saudi Arabia.

The US State Department designated the group a foreign terrorist organisation in 2012, freezing its assets in the United States and banning Americans from dealing with it.