Pakistani officials have ordered the detention of a firebrand cleric linked to the 2008 Mumbai terror attacks which killed 166 people.
Hafiz Saeed - who led the banned Lashkar-e Taiba (LeT) militant group and has a $10m (£5.8m) US bounty on his head - is under house arrest in Lahore.
His supporters protested in several Pakistani cities. He has repeatedly denied involvement in the attacks.
But India and the US say he helped plan the shooting and bombing massacre.
A spokesman for Mr Saeed claimed the Pakistani government had been pressured by the US to act against him.
There were small protests in response to his detention in cities including Lahore, Peshawar and Islamabad.
Mr Saeed heads Jamaat-ud-Dawa (JuD), a Pakistani charity group which India and the US say is a front for the LeT. It is listed as a terror outfit by the United Nations, and was put on a Pakistani terror watch list in 2015.
The cleric was taken by police from a mosque in Lahore on Monday and escorted to his residence to be placed under house arrest.
Four JuD members have also been placed in "preventative detention", according to an order by the interior ministry.
The Islamist leader's free movement in Pakistan has been a source of tension between Islamabad and Delhi for years, but it is unclear why the authorities decided to move against him now.
He was put under house arrest in 2008 after the bloodshed in Mumbai, but released about six months later. Pakistan maintained there was not enough evidence to put him on trial or hand him over to India.
The Mumbai carnage played out on live television as commandos battled the heavily armed attackers, who arrived by sea on the evening of 26 November, 2008.
The 10 gunmen killed commuters, tourists, and some of India's wealthy elite in a rampage that included attacks on two luxury hotels, a Jewish centre, and a train station.
It took the authorities three days to regain full control of the city.
Delhi believes there is evidence that "official agencies" in Pakistan were involved in plotting the attack - a charge Islamabad denies.
Another alleged LeT leader, Zakiur Rehman Lakhvi, was also accused of masterminding the attack. He was arrested in 2008 after India named him as a suspect but Pakistan freed him on bail in 2015.