The United States today said Pakistan has taken "some positive steps" since the Mumbai terror strikes even as it asked Islamabad [Images] to "act" to prevent "any future terrorist attacks".

"I think what we're seeing are some positive steps (from Pakistan). It's also 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....," state Department Spokesman Sean McCormack said in a briefing.

Earlier reports said Pakistani security forces launched a crack down on Lashker-e-Taiba (LeT), the militant outfit that India accused to be behind the November 26 Mumbai attacks.

Senior LeT commander and suspected Mumbai terror attacks [Images] mastermind Zakiur Rehman Lakhwi was among the 20 members arrested during a raid by army troops yesterday on a militant camp in Pakistan-occupied Kashmir(PoK).

However, Washington has called for more co-operation between Pakistan, India and the US, cautioning that the terrorists may plan "follow-on attacks".

"There's no doubt that Pakistan has taken some positive steps. But what's critically important now is that we continue to work together -- the Indians, the Pakistanis, the United States and our allies -- to prevent follow-on attacks after the attacks in  Mumbai," Press Secretary Dana Perino [Images] said in a separate briefing.

"It's always a concern once you have a terrorist attack that one of the things that you want is all the information you can get to prevent follow-on attacks, because we know that that's how some of these terrorists plan," she said.  

Asked whether the US had intelligence on more such strikes, Perino said: "I wouldn't say that."

"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," McCormack said.

"Let the Pakistan government describe for the public exactly what steps they're taking and what it is that they've done. We're going to be follow that situation very closely," the spokesman said when asked what specific measures would the US expect Islamabad to take.

He said Pakistan President Asif Ali Zardari [Images] called up US Secretary of State Condoleezza Rice [Images] to brief her on the actions taken by Islamabad against terror elements.

"Secretary Rice had earlier on her trips to India and Pakistan said that what's important is that those responsible for Mumbai attacks be brought to justice, that they not be allowed to in any way plan further or participate further in any violent actions, any terrorist actions," McCormack said.

The US reiterated that it is ready to assist India in the investigations into the Mumbai attacks and share informations in this regard.

"We ourselves learned through the experience after 9/11, information is key in preventing future terrorist attacks and to breaking up terrorist networks. So getting that information and sharing that information so that it can possibly be acted upon to prevent future attacks is vital," he said.

"We had to learn how to do this ourselves (gathering and sharing information) since 9/11, and that's part of what Secretary Rice did (promised) during her trip to India. She offered to the Indian government any assistance that they might be willing to accept," McCormack said.