United Nations: The United States is still pursuing the underground network established by Pakistani nuclear scientist A Q Khan across many nations, a top US official has said.

Assistant Undersecretary of State John R Bolton, who briefed the UN Security Council yesterday (Apr 27, 2004) on weapons of mass destruction, said Khan's network might have passed sensitive information to several nations.

Declining to name the countries that might have received the information, he however said the US was concerned about Iran and North Korea, which have nuclear technology.

The US was trying to collect details, he said.

"There are several others. There's a lot of information that we don't necessarily have corroboration for, but we are pursuing our concerns where we do have information, trying to get additional information, learning from others, and trying to assess the exact magnitude of the threat," he said.

Bolton said at least four countries are misusing Nuclear Non-Proliferation Treaty for developing nuclear weapons.

"States like Iran are actively violating their treaty obligations, and have gained access to technologies and materials for their nuclear weapons programs. North Korea violated its NPT obligations while a party, and then proved its strategic decision to seek nuclear weapons by withdrawing from the treaty entirely," he said.