The Obama [ Images ] administration has said that it is in constant touch with the Pakistani government in regard to disgraced Pakistani nuclear scientist A Q Khan who, it said, remained a nuclear non-proliferation concern.

"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 media-persons on Tuesday at his daily press briefing.

However, he refrained from making any comment on Khan's latest revelation that Pakistan had 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 had shared nuclear technology with these countries.