A former Bangladeshi Islamist party leader who was convicted of war crimes involving his country's 1971 independence war has died of a heart attack in a prison cell of a government hospital.

The 91-year-old Ghulam Azam died late Thursday after life support was removed at the Bangabandhu Sehikh Mujib Medical University in the capital, Dhaka.

A special tribunal last year sentenced Azam, a former chief of Jamaat-e-Islami party, to 90 years in jail on 61 charges of war crimes during Bangladesh war of independence from Pakistan.

Bangladesh accuses the Pakistani army and local collaborators for the deaths of 3 million people.

Azam led the party until 2000, and was still considered to be its spiritual leader. Jamaat-e-Islami claims his trial was politically motivated, which authorities deny.