The United States has expressed confidence in the safety of nuclear arsenals of India and Pakistan despite heightened tensions between the two neighbours in the wake of Mumbai terror attacks [Images] by a Pak-based terrorist outfit.

"Obviously, these are two nuclear powers. Whenever you are dealing with terrorism in countries that are nuclear powers, it is always -- it creates a heightened concern. Obviously, the Pakistani government has enormous challenges -- financially, politically, from terrorists," US Defence Department Spokesman Geoff Morrell said.

"We want to work with them and any others who find themselves in the situation, to make sure that their nuclear arsenals are always secure. We see no reason at this point to have any concern with regards to the security of either country's arsenal. So I think that's sort of where we are at this point," he added.

The senior Pentagon [Images] official would not get into the initial findings of the Mumbai attacks other than saying that there has been no direct request for US military assistance.

"To my knowledge, there have been no direct requests for US military assistance in really any of the efforts in the wake of the tragic Mumbai attacks. It is clear, based upon the fact you saw the chairman travel to both India and Pakistan last week that we take this problem very seriously and are in close coordination, discussion, consultation with the militaries in India and Pakistan," Morrell said.

"I am not going to get into what our level of discussions has been. I would suffice it to say that we are working closely with the Pakistani military, as we have before the Mumbai attacks. We are working closely with the Indian military, as we have as well for some time."

"But there have been no direct requests for assistance. We have channels and communication open, and are prepared to assist them should they need our assistance. I am not speaking in terms of inserting troops, but of in terms of providing any insight that we could help keep the situation as calm as possible in the wake of these attacks," the senior Defence official said.

"We are engaged with the militaries in both countries, as we always have been. You have obviously seen the chairman (of the Joint Chiefs of Staff) spending a great deal of time developing a relationship with General Kiyani, his counterpart in Pakistan. He obviously has relations with his counterpart in India.

"And that is, sort of, where we are at this point. We obviously are -- are watching things closely and you know, I think all, you know, are encouraging all the nations in the region to work together to prevent any future attacks, such as the, you know, the deadly one we saw over the Thanksgiving week in Mumbai," Morrell said.

"Whatever action the Pakistani military is taking against LeT, I'm not in a position to comment authoritatively on it, other than to say, we are watching them, we see it as a positive step, I think what all the problems that we have emanating from Pakistan terror-wise show us, is that this is a problem that needs to be dealt with on a sustained basis; that it can't be done in fits and starts, that there needs to be a constant and vigilant effort to go after the terrorist networks that exist there and throughout the region," he added.