Sufi Mohammad is the father-in-law of the Swat valley's Taliban leader
A radical cleric who brokered a failed peace deal in Pakistan's Swat valley has been arrested, officials say.
Sufi Mohammad was held in Peshawar in the north-west after being warned not to hold meetings there, officials said.
Provincial information minister Iftikhar Hussein told a news conference Sufi Mohammad had been detained for encouraging terrorism and violence.
The cleric negotiated a peace deal in February, widely seen as allowing the Taliban to take control of the valley.
Militants were allowed to impose Sharia law in the district in exchange for an end to two years of fighting.
However the deal later collapsed when Taliban fighters failed to disarm and moved into neighbouring districts.
"Instead of keeping his promises by taking steps for the sake of peace, and speaking out against terrorism, he did not utter a single word against terrorists," Mr Hussein told a news conference on Sunday.
He said that the influential cleric's stance "encouraged terrorism. It encouraged violence".
"He has been involved in activities which help militancy and militants and sabotage government efforts to combat them," Mr Hussein said.
The government's military operation to remove insurgents from the region displaced some two million people in Pakistan's north-west.
Pakistan's military says it has killed more than 1,600 militants in the offensive. The claim cannot be independently verified.
Sufi Mohammad is the founder of a banned militant group, Tehrik Nizam Shariat Mohammadi (TNSM).
He is also the father-in-law of the Taliban leader in the Swat valley, Maulana Fazlullah.
In June, two of Sufi Mohammad's aides - who were under arrest - were killed when militants attacked a convoy transporting prisoners to Peshawar, military officials said.
Maulana Fazlullah's whereabouts are unknown. The government says he was seriously hurt in an air strike but the Taliban have denied this, saying he is "alive and healthy".