Washington: Terming Pakistan as its "strongest" ally in the war against terror, the United States has said it wanted to build up and strengthen that country's institutions.

"We have helped Pakistan pull up entirely the nuclear proliferation network that was being run by Dr A Q Khan. Pakistan turned away from the Taliban because of US interest in getting them. And we are cooperating and working with Pakistan on anti-terrorist activities," US Secretary of State Colin Powell said.

"So what we want to do is build up and strengthen Pakistan's institutions," Powell told German TV in an interview.

When asked why the US was not attacking Pakistan since most of the "assassins" came from that country and it had become a "very dangerous mixture of nuclear weapons, fundamentalists and terrorists", Powell said Pakistan was its strongest ally.

"Why should we when we have the friendship with Pakistan...? Why should one attack one's strongest ally, when we are solving our problems in other ways?" he said.

"It is not necessary to attack every country that you might have a difference with at the moment. The reason we attacked Iraq was that Iraq had been continuing in this pattern of misbehaviour for 12 years," Powell said.