Pakistani security forces have arrested scores of members of a charity suspected to be linked to Lashkar-e-Taiba (LeT), the group blamed for the Mumbai attacks.
Rehman Malik, who holds ministerial rank in the interior ministry, said on Thursday that 124 people have been arrested.
"We are very, very serious" about fighting extremism, Malik told a press conference, saying the anti-terror fight was the "only option" for Pakistan.
The people arrested are members of Jamaat-ud-Dawa, one of the country's biggest charities, but which is widely viewed as the political wing of the LeT, banned in Pakistan since an attack on the Indian parliament in late 2001.
The crackdown came in response to a UN Security Council resolution passed last month, describing Jamaat-ud-Dawa as a "terror group".
Malik also said that Islamabad needed more information from India in order to proceed with its own investigations into last November's attack on the Indian financial capital.
"This is the time that Pakistan and India need to stick together," he said. "We'll be needing more information."
More than 170 people died when several locations in Mumbai, including two famous hotels, came under simultaneous attacks.