WASHINGTON - Despite Pakistans repeated assurances that its nuclear weapons are in safe hands, American officials say they are increasingly concerned over the security of Pakistans atomic arsenal amid widening influence of the Taliban and al-Qaeda, US officials said. Senior US officials say they are becoming more concerned about the possibility of militants might hijack a weapon or infiltrate laboratories or nuclear fuel-producing installations, The New York Times reported Monday. The officials said there is no reason to suspect an imminent threat against the arsenal, the newspaper said. President Barack Obama said last week he has confidence the security of the nuclear infrastructure is a top priority of Pakistani military officials. However, US officials do not know the location of all of Pakistans nuclear sites, and are less comfortable than they had been with Pakistani assurances the nuclear arsenal is safe while Pakistani officials have declined to provide more information on such details about the nuclear arsenal as locations and security plans, paper said. We are largely relying on assurances, the same guarantee we have been hearing for years, said a senior official whose name was not reported. The worse things get, the more strongly they hew to the line, 'Dont worry, weve got it under control. The issue could come up this week when President Zardari meets in Washington with Obama, the Times said. Pakistanis, however, have continued to rebuff American requests for more details about the location and security of the countrys nuclear sites, the report noted. Some of Pakistans reluctance stemmed from longstanding concern that the US might be tempted to seize or destroy the nations arsenal if the insurgency spread further, paper maintained. The Obama administration inherited from President George W Bush a multiyear, $100 million secret American programme to help Pakistan build stronger physical protections around some of those facilities, and to train Pakistanis in nuclear security, the Times dispatch pointed out. But much of that effort has now petered out, it said, and American officials have never been permitted to see how much of the money was spent, the facilities where the weapons are kept or even a tally of how many Pakistan has produced. The facility Pakistan was supposed to build to conduct its own training exercises is running years behind schedule. The Times said, Mr Zardari heads the countrys National Command Authority, the mix of political, military and intelligence leaders responsible for its arsenal of 60 to 100 nuclear weapons. But in reality, his command and control over the weapons are considered tenuous at best; that power lies primarily in the hands of the army chief of staff, Gen Ashfaq Parvez Kayani. For years the Pakistanis have waved away the recurring American concerns, with the head of nuclear security for the country, Gen Khalid Kidwai, dismissing them as 'overblown rhetoric.