Police in India have held an Islamic cleric in connection with blasts that hit the city of Bangalore in mid-2008.
Abdul Nasser Madani was arrested at his home in the state of Kerala.
He accuses the Hindu nationalist Bharatiya Janata Party (BJP) government in Karnataka, whose capital is Bangalore, of "framing" him.
One woman was killed and several others injured in July 2008 when seven bombs hit crowded areas of the city, which is India's information technology hub.
Bangalore Police Commissioner Shankar Bidri said Mr Madani would be taken to court.
Police said Mr Madani was present at a meeting to plan the bombings, but he denies any role and is seeking bail.
The arrest prompted protests in Muslim-dominated parts of Kerala, with groups saying Mr Madani is being targeted by the BJP-ruled government of Karnataka - police deny this.
Mr Madani heads the Peoples' Democratic Party (PDP), which champions the cause of minorities and Dalits [low-caste Hindus].
A police team from Bangalore had to wait for a week in Kerala before making the arrest on Tuesday.
Karnataka Home Minister VS Acharya had blamed Kerala's Communist government for delaying Mr Madani's arrest.
Correspondents say the government in Kerala treaded cautiously, fearing a backlash from Mr Madani's supporters.
He founded the PDP after the demolition of the disputed Babri mosque in northern India by Hindu hardliners in 1992.
He was arrested for his role in the 1998 blasts in Coimbatore, in the southern Tamil Nadu state, in which at least 60 people were killed.
He was acquitted of all charges in 2007.