US Ambassador to India David C Mulford said the dossier contains extensive inputs from the Federal Bureau of Investigation (FBI).

"From what I have seen it is a very credible material. The FBI is cooperating in Mumbai...It is information which tells and gives a very accurate account of what has happened," he told Karan Thapar's programme 'Devil's Advocate'.

Commenting on the Indo-US cooperation in this area, he said the dossier prepared by India extensively used material provided by the FBI. "As far as I see, it (FBI material) was used extensively because the material was same."

Underlining the credible aspect of the dossier, he said, "As far as the FBI is concerned, they do not deal with non-credible material. It is a truly professional organisation supported by absolutely high-tech techniques."

On the Mumbai attacks, Mulford said "there were handlers who were in touch with these people on the ground. It is a serious problem. This act of terrorism came from Pakistan".

When referred to Prime Minister Manmohan Singh's view that "official agencies" of Pakistan could have been involved in the terror strikes, the Ambassador said "I think one needs to be very very careful about making those kinds of allegations unless you have very concrete evidence to that degree of specificity."

The US Ambassador said his country cannot get into "that kind of specificity unless there is some justification for it."

Mulford said that there are a lot of things that tell that "this is a very serious situation. You don't need to know that degree of specificity that you need to compel to pursue the matter."

Emphasising that Pakistan has a "serious problem on its hand", he said "you don't need some kind of a definitive state to know that you have a definite problem on hand."

When referred to Pakistan's virtual rejection of the credibility of evidence within 24 hours after getting it, he said, "Well, I don't think you can cut some quick reaction on the statement of one particular individual. I think it takes some time. You have, after all, a situation where there is a civilian government, a very strong military, a very strong intelligence agency and a media and other players.

"And I think you have to take a view that it is going to take little time to percolate to see what really is the outcome."

He went on to add that "Somebody in denial (mode) doesn't necessarily remain in denial and isn't always on specific point in denial even if they are projecting a sense of denial."

Mulford said "It is complex and you would be mistaken to seize on a statement that is particularly irritating to you or proves a point of some kind to you that are standing back waiting and seeing the effort it is achieving."

Mulford said "It is complex and you would be mistaken to seize on a statement that is particularly irritating to you or proves a point of some kind to you that are standing back waiting and seeing the effort it is achieving."

He said the US view was that the Pakistani government has "responded cooperatively with us".

Insisting that Pakistan is "very concerned" about the situation, the Ambassador said "they (Pakistan) have made some efforts early on to offer a delegation to come to India to cooperate and exchange information which is not being accepted and they have recently agreed to hand over information and cooperate with the government here.

"The question is what is the level of cooperation going to be. How forthcoming is it? Is it enough to satisfy people here of their credibility of the party to cooperate with."

He said one should not "get lost with some of the detail ... because I think we all understand there has to be a level of cooperation to move from here."

Asked how long India should wait for Pakistan to respond, he said "it is not a question of time, although time is important, because to get into a situation where so much time passes, it makes them look uncooperative.

"But you do have to sort of gauge what is happening, what their own situation is and what sort of problems they are facing. And don't forget, the US is in regular touch with them because of its own losses."

The US Ambassador said "if you have to make progress, you have to make some element of cooperation and that means looking at ways to accomplish some minimal levels.

On Pakistan's offer of sending a high-level delegation, he noted that it was made with no detail as to who would be on the delegation and it was never filled out with additional information. "So, I don't think India made a mistake to not take that up because it wasn't going anywhere."

Asked how much time should be given by New Delhi to Islamabad to evaluate evidence, Mulford said it was for the Indian government to decide.