Pakistan's army says it has arrested senior associates of the radical Islamist cleric, Sufi Mohammad, in the north-west of the country.
Six men, including Sufi Mohammad's deputy Maulana Mohammed Alim, have been detained, officials said.
Mr Mohammad is the father-in-law of the Taliban leader in the Swat valley where the army is battling Taliban militants.
The arrests come as US envoy Richard Holbrooke is in the region to visit people displaced by the fighting.
"Following a tip-off, the security forces raided a madrassa [seminary] located in Aman Darra area," the army said in a statement late on Thursday night.
In addition to Sufi Mohammad's deputy, the security forces also detained his spokesman Ameer Izzat Khan, and another aide, Syed Wahab.
The statement also said that three Afghan nationals were arrested in the raid. Officers seized eight hand grenades and other explosives from the site
See a map of the region
The BBC's M Ilyas Khan in Islamabad says these are the only significant arrests since the army launched its latest operation against militants in the Swat region one month ago.
However the arrested aides had not been in hiding and could regularly be found at their party headquarters. It is not known exactly why they have been picked up now and not earlier, he says.
'Whereabouts unknown'
Our correspondent adds that the arrests come at a time of acute public anxiety about the progress of the conflict in the Swat valley.
While the army has been vocal about the number of Taliban militants killed, there has been no word about the location and fate of senior militant leaders.
Sufi Mohammad was instrumental in brokering the peace deal between the Taliban and the government imposing Sharia law in the district. This later fell apart, when Taliban fighters moved into neighbouring districts.
He is also the founder of a banned militant group, Tehrik Nizam Shariat Mohammadi (TNSM).
In the past the organisation has distanced itself from the actions of Sufi Mohammad's son-in-law, Maulana Fazlullah, the Taliban leader in Swat.
But, our corresondent says, Mr Mohammad and his followers have been at the forefront of elements in Swat criticising the Pakistani government for its slowness in imposing Sharia law when the deal between the government and the Taliban was still in place.
Sources close to Mohammad Sufi say that his whereabouts have been unknown for the past three or four days.
Two of his sons, Ziaullah and Rizwanullah, are also said to be missing.
Pakistan's army chief, General Ashfaq Kayani, said in a statement last night that the army had "turned the tide" against the Taliban and reiterated that the army aimed to completely eradicate them from the Swat valley.
A senior army officer has said the offensive to eject the Taliban from the Swat valley could take another two months to complete.
The army says several former militant strongholds are now under its control.
A statement on Wednesday said Charbagh - about 20km (12 miles) north of Mingora, the main town in Swat valley - had been retaken.
Troops had also "successfully secured Pir Baba and Bhai Kalay" in neighbouring Buner district, where heavy fighting has gone on for weeks.
More than two million people have been displaced by the fighting.
Six men, including Sufi Mohammad's deputy Maulana Mohammed Alim, have been detained, officials said.
Mr Mohammad is the father-in-law of the Taliban leader in the Swat valley where the army is battling Taliban militants.
The arrests come as US envoy Richard Holbrooke is in the region to visit people displaced by the fighting.
"Following a tip-off, the security forces raided a madrassa [seminary] located in Aman Darra area," the army said in a statement late on Thursday night.
In addition to Sufi Mohammad's deputy, the security forces also detained his spokesman Ameer Izzat Khan, and another aide, Syed Wahab.
The statement also said that three Afghan nationals were arrested in the raid. Officers seized eight hand grenades and other explosives from the site
See a map of the region
The BBC's M Ilyas Khan in Islamabad says these are the only significant arrests since the army launched its latest operation against militants in the Swat region one month ago.
However the arrested aides had not been in hiding and could regularly be found at their party headquarters. It is not known exactly why they have been picked up now and not earlier, he says.
'Whereabouts unknown'
Our correspondent adds that the arrests come at a time of acute public anxiety about the progress of the conflict in the Swat valley.
While the army has been vocal about the number of Taliban militants killed, there has been no word about the location and fate of senior militant leaders.
Sufi Mohammad was instrumental in brokering the peace deal between the Taliban and the government imposing Sharia law in the district. This later fell apart, when Taliban fighters moved into neighbouring districts.
He is also the founder of a banned militant group, Tehrik Nizam Shariat Mohammadi (TNSM).
In the past the organisation has distanced itself from the actions of Sufi Mohammad's son-in-law, Maulana Fazlullah, the Taliban leader in Swat.
But, our corresondent says, Mr Mohammad and his followers have been at the forefront of elements in Swat criticising the Pakistani government for its slowness in imposing Sharia law when the deal between the government and the Taliban was still in place.
Sources close to Mohammad Sufi say that his whereabouts have been unknown for the past three or four days.
Two of his sons, Ziaullah and Rizwanullah, are also said to be missing.
Pakistan's army chief, General Ashfaq Kayani, said in a statement last night that the army had "turned the tide" against the Taliban and reiterated that the army aimed to completely eradicate them from the Swat valley.
A senior army officer has said the offensive to eject the Taliban from the Swat valley could take another two months to complete.
The army says several former militant strongholds are now under its control.
A statement on Wednesday said Charbagh - about 20km (12 miles) north of Mingora, the main town in Swat valley - had been retaken.
Troops had also "successfully secured Pir Baba and Bhai Kalay" in neighbouring Buner district, where heavy fighting has gone on for weeks.
More than two million people have been displaced by the fighting.
