Pakistan is under intense pressure to act against militants
Pakistan has arrested leading militants following the Mumbai attacks but says it will not hand them over to India.
Defence Minister Ahmad Mukhtar said Jaish-e-Mohammad founder Masood Azhar and Lashkar-e-Taiba commander Zaki-ur-Rehman Lakhvi had been held.
His comments came as Pakistan's foreign minister said his country did not want war but was "fully prepared".
Delhi says the Mumbai gunmen are linked to Pakistan, which is under intense Indian and US pressure to take action.
Meanwhile, Pakistani President Asif Ali Zardari says peace talks with India must proceed to "foil the designs of the terrorists".
"Pakistan is committed to the pursuit, arrest, trial and punishment of anyone involved in these heinous attacks," he wrote in the New York Times on Tuesday.
On Monday, the US praised what it said were "positive steps" after Pakistani forces raided a camp in Pakistani-administered Kashmir used by Lashkar-e-Taiba, which India links to the attacks.
But state department spokesman Sean McCormack also 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".
Delhi has not commented on the operation.
Zaki-ur-Rehman Lakhvi is the Lashkar commander India suspects of planning the Mumbai attacks.
"Lakhvi was picked up yesterday. Azhar has also been picked up," Mr Mukhtar told India's CNN-IBN channel.
He also repeated Islamabad's request for evidence to be shared with Pakistan.
"Both US and India say they have ample proof but why is it hidden from us?" Mr Mukhtar asked.
Foreign Minister Shah Mehmood Qureshi, meanwhile, repeated that Pakistan would not hand over to India any of its citizens arrested in connection with last month's attack.
He said that about 16 people had been detained for questioning so far in a crackdown against banned Islamist groups like Lashkar-e-Taiba.
Reports say Pakistani police have also ordered the sealing of some offices used by Jamaat-ud-Dawa, the Islamic charity seen as a front for Lashkar-e-Taiba.
Mr Qureshi added: "We do not want to impose war, but we are fully prepared in case war is imposed on us. We are not oblivious to our responsibilities to defend our homeland."
Tensions between the countries have been steadily rising since the attacks last month, which left at least 170 people dead. Some of the gunmen are said to have had links to Pakistani militants. Islamabad denies any involvement.
Masood Azhar is one of the most wanted men in India. The group he founded, Jaish-e-Mohammad, is accused along with Lashkar-e-Taiba of taking part in the attack on India's parliament in 2001 which led the two countries to the brink of war.
Mr Azhar is reportedly on a list of people Delhi has demanded Pakistan hand over.
The BBC's Syed Shoaib Hasan in Karachi says Mr Azhar has been in and out of Pakistani custody over the past five years.
Our correspondent says he is no longer considered to be in day-to-day charge of Jaish-e-Mohammad and detaining him will make little difference to militant activity.
The group is thought to behind a string of attacks inside Pakistan as well.
Witnesses say the camp raided on Sunday by Pakistani security forces, at Shawai on the outskirts of Muzaffarabad, is run by Jamaat-ud-Dawa.
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.
Several other people were also reportedly held, as well as Mr Lakhvi.
Indian investigators have said that the only gunman captured in Mumbai, named as Azam Amir Qasab, was indoctrinated by Lashkar-e-Taiba (Soldiers of the Pure), and trained at a camp run by the group.
Some media reports have suggested that truth serum may be used as part of his interrogation.
Although the authorities in Pakistan formally banned Lashkar six years ago and curbed its activities, its camps were never closed.
Analysts say that as long as the army continues a policy of using proxies to fight regional battles, Pakistan's security establishment will be reluctant to shut Lashkar-e-Taiba down.