The Obama Administration has said disgraced Pakistani nuclear scientist A Q Khan remains a nuclear non-proliferation concern and it is in constant contact with Pak authorities in this regard.
"We have said consistently that we have real concerns about Mr A Q Khan. We believe that he remains a risk for proliferation," the State Department spokesman, Ian Kelly, told reporters on Tuesday at his daily press briefing.
However, he refrained from making any comment on the Khan's latest revelation that Pakistan supplied nuclear know-how to countries such as China, Iran, Libya and North Korea.
Britain's Sunday Times, quoting a four-page 'secret' letter from Khan addressed to his Dutch wife Henny, had said that Pakistan shared nuclear technology with these countries.
As Khan remains a real concern for the US, Kelly said, "For that reason, we stay in very close contact with the Pakistani authorities to ensure that there is no proliferation risk from him or from any other source in Pakistan."