Days after Prime Minister Manmohan Singh [Images] said that Pakistan's official agencies could be involved in Mumbai terror attacks, the US today said "accusations" should not be made without evidence.

"I don't think we want to take a view that we make accusations against certain parties without the usual evidences, proofs," Ambassador [Images] David C Mulford said when asked whether the US agrees with Singh that Pakistan's official agencies could have had a role in the Mumbai attacks.

He said the US was determined to work "non-stop" and "as long as it takes" to ensure that the perpetrators of the Mumbai terror attacks [Images] are brought to justice.

 "When Americans are killed anywhere, we pursue those people and that is what we are up to in Pakistan. We will press ahead and we will do it non-stop as long as it takes," he said at an interaction here.

The US has been pressing for deeper understanding in Pakistan of the roots of the problem of terrorism, he said, adding that "(by) learning more and more I hope that we can bring the people who committed this heinous act to book.

An important aspect of the US relationship with Pakistan is to see it succeed and not become a failed state, he said.

"Like India, we have a common agenda -- we want to see Pakistan succeed, not fail, not become a serious problem, not become a failed state. That is the American agenda," said Mulford, who has been asked to stay on as the Ambassador here for some more time even after the Obama [Images] Administration takes charge.