"When Americans are killed anywhere, we pursue those people and that is what we are upto in Pakistan. We will press ahead and we will do it non-stop as long as it takes," US Ambassador David C Mulford said at an interaction in New Delhi.

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.

Mulford made it clear that the US does not want to make accusations against "certain parties" without evidence. "I don't think we want to take a view that we make accusations against certain parties without the usual evidences, proofs," he said without elaborating. Mulford said an important aspect of the US relationship with Pakistan was to see it succeed and not become a failed state.