Sources said that Mattu, who is also the spokesperson of the Jammu and Kashmir People's Conference, was in Delhi for medical treatment. The Centre had restricted his movements in the days following its decision to scrap Jammu and Kashmir's special status on August 5.
In an interview to a media organisation, Mattu on Monday had criticised the ongoing clampdown on Kashmir and the detention of its political leaders, and his party's plan to challenge abrogation of Article 370 in the Supreme Court.
He had said that while there may not be any dead bodies lying on the streets, assuming that Kashmir has returned to normal would be highly unrealistic.
"While the communication blackout has created a situation where specifics are speculative, it is safe to assume the ground situation can't possibly be anywhere near normal. The media and administrative narrative seem content in defining 'normalcy' in a purely operational context," Mattu had said.
"We have consulted senior-most constitutional experts and luminaries and will be contesting the move in the Supreme Court. Our party Chairman (Sajjad Gani Lone) has, before he was arrested, appealed to the people to maintain calm and not resort to any violent means of expressing their anguish and sense of loss."
( With inputs from IANS )