The US has said that Pakistan had taken "some positive steps" in helping India probe the attacks in Mumbai.
Pakistan says it has arrested two leading militants as tensions with India continue over the Mumbai attacks.
On Monday, Pakistani forces swooped on a camp in Pakistani-administered Kashmir used by a militant group that India links to the attacks.
Defence Minister Ahmad Mukhtar said Lashkar-e-Taiba operations chief Zaki-ur-Rehman Lakhvi and Jaish-e-Mohammad chief Masood Azhar were held on Monday.
The Lashkar-e-Taiba group's operational chief, Zaki-ur-Rehman Lakhvi, who is said by Delhi to have ordered the attacks, was reportedly seized.
"Lakhvi was picked up yesterday. Azhar has also been picked up," he told India's CNN-IBN channel.
The US said it was "following the situation very closely" in Pakistan.
India says the Mumbai gunmen are linked to Pakistan, which is under intense Indian and US pressure to take action.
US State Department Sean McCormack told reporters: "I think what we are seeing are some positive steps. I'll let the Pakistani government describe in more detail what those are and what actions they are taking."
On Monday, the US praised what it said were "positive steps" after Pakistani forces swooped on a camp in Pakistani-administered Kashmir used by Lashkar-e-Taiba, a militant group that India links to the attacks.
He said it was "incumbent upon the Pakistani government to act to prevent any future terrorist attacks, to break up those networks that may be responsible for perpetrating acts of violent extremism".
US state department Sean McCormack said it was "incumbent upon the Pakistani government to act to prevent any future terrorist attacks, to break up those networks that may be responsible for perpetrating acts of violent extremism".
"What we don't want to see are future attacks emanating from Pakistani soil. And we would urge cooperation among all interested parties to make sure that that doesn't happen," he said.
"What we don't want to see are future attacks emanating from Pakistani soil. And we would urge co-operation among all interested parties to make sure that that doesn't happen," he said.
Last week, US Secretary of State Condoleezza Rice urged Islamabad to mount a "robust" and "effective" response to the attacks in Mumbai.
Mr McCormack said that Ms Rice had offered the Indian government "any assistance that they might be willing to accept and listen to any advice that we might be able to provide as we have built this experience up over time and we have had some success in that regard".
A White House spokeswoman has also praised Pakistan for taking action against militants.
"I think there is no doubt that Pakistan has taken some positive steps," Dana Perino said.
Witnesses say the camp raided by Pakistani security forces, at Shawai on the outskirts of Muzaffarabad, is run by the Islamic charity Jamaat-ud-Dawa, widely seen as a front for Lashkar-e-Taiba, which was banned in 2002.
Witnesses say the camp raided by Pakistani security forces, at Shawai on the outskirts of Muzaffarabad, is run by the Islamic charity Jamaat-ud-Dawa, widely seen as a front for Lashkar-e-Taiba, which was banned in 2002.
Local residents said the army had blown up buildings at the camp, which has an office, religious school and a residential area housing about 150 people.
Local residents said the army blew up buildings at the camp, which has an office, religious school and a residential area housing about 150 people.
Government and militant-related sources in the capital Islamabad and in the Kashmiri city of Muzaffarabad reported Mr Lakhvi's detention although there has been no official confirmation.
BBC correspondents say it is unlikely anyone detained in Pakistan will be handed over to India and any trial would probably take place in Pakistan.
The BBC's Barbara Plett in Islamabad says that if the reports prove to be true, it is unlikely Mr Lakhvi will be handed over to India and any trial will probably take place in Pakistan.
The government has been under tremendous Indian and American pressure to act on allegations that the Mumbai atrocities were linked to Pakistan, she adds.
