Indonesian authorities detained Muslim cleric Abu Bakar Bashir on Monday morning for his latest terror-related activities.
Anti-terrorism police arrested Bashir, 71, his wife, driver and another woman as they were driving to his home near Solo in central Java.
Over the weekend, police carried out raids in West Java, arresting five terror suspects and confiscating explosive material.
Authorities have been tagging Bashir since discovering a new terror training camp in Aceh last February.
Police believe the cell, which calls itself al-Qaeda Aceh, has been plotting the assassination of Indonesian President Susilo Bambang Yudhoyono.
The president said on Saturday that police prevented an attack against him during a visit to the province.
Authorities also believe al-Qaeda Aceh is planning to target foreigners in Mumbai-style bombings.
Bashir is the founder and spiritual leader of Jema'ah Ansharut Tauhid, an al-Qaeda-linked group that carried out the 2002 bombings on the island of Bali, which killed 202 people, many of whom were foreign nationals.
Bashir also founded the Ngruki boarding school in East Java, where he is believed to have recruited and counseled students to take part in the Bali bombings.
Bashier spent 26 months in prison on conspiracy charges, but was released in 2006.
His history in Islamic terrorism dates back to the 1980s when he was imprisoned for advocating that Indonesia become an Islamic state.