Pakistani security forces raided a camp used by Lashkar-e-Taiba militants in Pakistani Kashmir on Sunday, a witness and an official from a charity linked to Lashkar said.
"This happened this afternoon, security forces took over the camp," an official with Jamaat-ud-Dawa charity told Reuters.
A resident close to the camp on the outskirts of Muzaffarabad said he had seen security forces raid it.
The charity official said there were fighters there from Lashkar, the prime suspect in the attacks on Mumbai last month that killed at least 172 people.
There has been no confirmation of the reports from Pakistani officials.
The Lashkar-e-Taiba group has been blamed for earlier attacks including a 2001 assault on India's parliament.
It was formed with the help of Pakistan's intelligence agencies to fight Indian rule in Kashmir, but analysts say it is now part of a global jihadi network sympathetic to al Qaeda and may have direct ties with the al Qaeda network.
Mumbai militants used Pakistani soil - Rice
US Secretary of State Condoleezza Rice said Pakistan territory was used to the Mumbai attacks, and again urged Islamabad to help bring perpetrators to justice.
Pakistan has called for India to back up its charges of Pakistani involvement with proof.
But in interviews with US television networks, Rice said there was no doubt the militants behind the Mumbai attack had operated from Pakistani soil, although she said probably "non-state" actors were involved.
With Islamabad's ties with Washington as well as with India at stake, Pakistan must take action against the militants, Rice said.
Pakistan is a long-time US ally that has received billions in US aid to root out militant groups.
India has blamed Islamist militants based in Pakistan for the three-day assault on India's commercial capital that killed at least 170 people.
Pakistan has condemned the attacks, denied any involvement by its state agencies and vowed full cooperation in investigations. It has called for evidence from New Delhi about any Pakistani role in the assault.
Surviving Mumbai gunman
More details have emerged about the suspect held as the sole surviving gunman from the attacks mounted Mumbai on 26 November.
A senior Indian police investigator says Ajmal Amir Kasab was a petty criminal who was indoctrinated by Lashkar-e-Taiba and trained in various locations, including Pakistani-administered Kashmir.
The government in Islamabad says it has received no hard evidence that any of the attackers were from Pakistan.