Radical Indonesian cleric Abu Bakar Bashir was sentenced to 15 years in prison Thursday. The 72-year-old religious leader was convicted of terrorism.

Bashir is thought to be the spiritual leader of Indonesia's Jemaah Islamiyah, a terrorist group linked to al Qaeda and the September 11 attacks.

Bashir was arrested in 2010 during a raid on a terrorist training camp in Aceh, Indonesia. He was also charged with funding Jemaah Islamiyah.

The cleric continues to insist on his innocence, and says that the trial was unjust.

This verdict ignores Sharia law and is based on the infidel law, so it's forbidden for me to accept it, Bashir said in a statement.

Bashir's lawyers will appeal the verdict.

Jemaah Islamiyah has been behind a significant number of the terrorist attacks in Indonesia, and Bashir is considered to be connected to the 2002 bombing of a Bali nightclub, which killed more than 200 people. Bashir was tried for his involvement in the bombing, but was excused of the charges in 2006.

In anticipation of related civil unrest, around 3,000 police and security forces surrounded the Jakarta courthouse, according to Businessweek. Supporters of Bashir gathered outside, chanting God is great, and Free Ustadz Abu Bakar Ba'asyir.

Bashir is also suspect of a 2008 bombing in Mumbai, India that killed hundreds.