ISLAMABAD, Pakistan (CNN) -- Pakistan's president has said it took three years before he got convincing proof from the U.S. that a top nuclear scientist was selling weapons technology.

President Pervez Musharraf had suspected for years that Abdul Qadeer Khan was spreading nuclear secrets to Iran, Libya and North Korea, he told the New York Times.

"If they knew it earlier, they should have told us," he said. "Maybe a lot of things would not have happened."

Khan's opulent lifestyle reportedly raised suspicions years before the government was compelled to take action, The Associated Press quotes a Pakistani government official as saying. (Full story)

Meanwhile, U.S. Secretary of State Colin Powell has publicly urged Pakistan to "pull up by the roots" the illegal proliferation of nuclear technology.

The United States is interested in learning all it can about Pakistan's nuclear scandal, Powell said, and has called for an end to the exchange network set up by Khan.

But Powell says it is up to Pakistan to decide how it deals with him.

"Although (Khan) has made some mistakes for which I am regretful, he is our national hero so I grant Dr Khan pardon," Musharraf said last week.

It is arguably one of the president's most difficult crises since coming to power in a 1999 military coup.

Khan had confessed to supplying nuclear know-how to countries listed on U.S. President George W. Bush's axis of evil. The White House, however, has avoided criticizing Musharraf and has stood by his decision to pardon Khan.

"The action he took with respect to pardoning Mr. Khan is something that he felt was appropriate for him to do and he has explained his position thoroughly," Powell has said.

The investigation into Khan's leaks was sparked by information from U.S. intelligence, according to officials. (CIA 'sparked nuke probe')

Islamabad has said it will share the findings of the investigation with the U.N.'s International Atomic Energy Agency.

Foreign Minister Khurshid Mahmud Kasuri has said Pakistan would cooperate with the IAEA in "every conceivable way" as "responsible members of the international community." (Pakistan pledges cooperation)

However, Pakistan has said it will not allow the U.N. to inspect its nuclear facilities and refuses to hand over any documents from the investigation.

Still, the international community appears satisfied.

"Obviously it is a very difficult situation (Musharraf) has to deal with," U.N. Secretary General Kofi Annan has said. "He is dealing with a national hero."

"He has given the assurances ... that they are going to take every measure to ensure that this sort of trafficking does not take place."

Musharraf is a key U.S. ally in the war on terror in neighboring Afghanistan and border regions where Osama bin Laden is believed to be hiding.

But his alliance with Washington has drawn strong criticism at home, and Islamic extremists were blamed for two assassination attempts against Musharraf in December.

"I think the chapter is closed," Pakistani Senator Mushahid Hussain told CNN.

"You're talking about 2004. President Bush is keen on only one thing -- his re-election -- and he needs Pakistan very badly for that. For Taliban, for Osama bin Laden, for stability in Afghanistan.

"Pakistan is too pivotal an ally for America in the present situation."

Observers say Washington's easy acceptance of the pardon has everything to do with timing.

Bush can only push his Pakistani counterpart so far, they say, and still hope for full cooperation in dismantling the nuclear proliferation black market and a final push to catch Osama bin Laden in the northern spring.

-- CNN's Islamabad Bureau Chief Ash-har Quraishi contributed to this report