Pakistani ex-President Pervez Musharraf has been arrested over a 2007 mosque raid a day after the country's supreme court granted him bail in another case.
The operation ordered by Gen Musharraf on Islamabad's besieged Red Mosque left a cleric and more than 100 others dead.
Gen Musharraf is already under house arrest on other charges, but appeared to take a step towards freedom after he was granted bail on Thursday.
He insists all the charges against him are politically motivated.
"We are confident that truth will prevail and all these false, fabricated and fictitious charges against the former president will have no legs to stand on," Gen Musharraf's spokesman Raza Bokhari said on Thursday.
Gen Musharraf is facing murder trials over the assassination of Benazir Bhutto and a Baloch tribal leader. He has been bailed in both cases.
He also faces charges over his attempt to sack Pakistan's higher judiciary in 2007. The current government has said it will try him for treason.
Thursday's arrest is believed to relate to the death of radical cleric Abdul Rashid Ghazi who was killed when Pakistani troops stormed the mosque after a stand-off with hardline Islamists barricaded inside.
"We have put Gen Musharraf under house arrest in a case involving a military operation on an Islamabad mosque," said senior police official Muhammad Rizwan, according to AFP news agency.
"We will present him before a court on Friday," he added.
Gen Musharraf has been in custody since April after he was hit with a series of charges relating to his 1999-2008 rule shortly after returning from self-imposed exile to contest a general election, won by Nawaz Sharif's party.
The general had come to power in 1999 when he ousted Mr Sharif, who was prime minister at the time, in a bloodless coup.
After he was defeated by Benazir Bhutto's party in 2008, he left Pakistan to live in self-imposed exile in Dubai and London.