Pressure is building on Capitol Hill to find out whether Pakistani officials knew about Usama bin Laden's location on the outskirts of a military town and withheld that information from Americans for years.

Bin Laden could have been living in his $1 million house on a sprawling compound in northern Pakistan for as long as six years, according to the White House. Secretary of State Hillary Clinton and other U.S. officials have stressed that Pakistani cooperation helped lead Americans to the Al Qaeda leader and that the U.S.-Pakistan alliance must continue.

But with that alliance already fraying, U.S. lawmakers say the burden is on Pakistan to prove it was not complicit in keeping bin Laden's location under wraps. Trust between the two governments was clearly an issue in the run-up to the mission, with top officials suggesting they were concerned some in Islamabad could blow their cover. CIA chief Leon Panetta, in a blunt assessment, said in an interview with Time that it was decided "any effort to work with the Pakistanis could jeopardize the mission" because they "might alert the targets."

After bin Laden was killed, Sen. Bob Corker, R-Tenn., sent a letter to Clinton requesting details on the "extent of the cooperation" from the Pakistanis. He questioned how the terror mastermind hid in such a relatively prominent location.

"The discovery that bin Laden was living in comfortable surroundings merely 35 miles from Islamabad calls into question whether or not the Pakistanis had knowledge that he was there and did not share that knowledge. The claim had been he was difficult to find because he was hiding in the mountains," he wrote.

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Rep. Ted Poe, R-Texas, plans to introduce legislation this week to freeze U.S. aid to Pakistan "unless the State Department can certify to Congress that Pakistan was not harboring America's number one enemy."

Sen. Frank Lautenberg, D-N.J., similarly called for more information on what Pakistan knew before they can receive the $3 billion in foreign aid requested for Pakistan in 2012, and potentially more in additional military funding.

Pakistan's government has rejected these concerns.

In the nation's first formal response to the suspicions, Pakistani President Asif Ali Zardari denied suggestions that his country's security forces may have sheltered the terrorist, and said that Pakistan's cooperation with the U.S. helped to pinpoint him.

"Some in the U.S. press have suggested that Pakistan lacked vitality in its pursuit of terrorism, or, worse yet: that we were disingenuous and actually protected the terrorists we claimed to be pursuing. Such baseless speculation may make exciting cable news, but it doesn't reflect fact," Zardari wrote in a Washington Post opinion piece.

Former Pakistani President Pervez Musharraf also told Fox News there is "no basis" for claiming the Pakistani intelligence service shielded bin Laden. He said it would have been "utterly stupid" for the ISI to locate him in such a prominent place.

"That is not something the ISI would have done. Certainly not. So let's not accuse the ISI," he told Fox News.

Musharraf also accused the United States of violating Pakistani sovereignty. But while he insisted most Pakistanis are moderates and relieved bin Laden is dead, pro-bin Laden sentiment was on display.

Hundreds of people reportedly took to the streets in Quetta, Pakistan, on Monday to show support for bin Laden and oppose the American action.

Officials in the Obama administration and aides to former President George W. Bush both say the relationship with Pakistan is an important one.

"It's possible, I suppose, that they did not know" bin Laden was hiding in plain sight, former Secretary of State Condoleezza Rice told Fox News. She said Pakistan has also suffered at the hands of terrorists, losing Prime Minister Benazir Bhutto. Rice said the Pakistanis should want to know how bin Laden could have hidden in the compound for so long.

White House counterterrorism adviser John Brennan also said "Pakistan has been responsible for capturing and killing more terrorists inside of Pakistan than any country, and it's by a wide margin."

Still, he said U.S. officials are studying "how he was able to hold out there for so long, and whether or not there was any type of support system within Pakistan." He said it's "inconceivable" to think bin Laden did not have a support system.

He said no one in Pakistan was told about the intelligence leading to bin Laden or the mission to capture or kill him, an indication there were concerns bin Laden would be tipped off.

He said Pakistan was not informed until after U.S. forces were out of Pakistani airspace, and that there were concerns about getting out of that airspace before Pakistan responded.

"At the time, the Pakistanis were reacting to an incident that they knew was taking place in Abbottabad," he said Monday. "Therefore, they were scrambling some of their assets. Clearly, we were concerned that if the Pakistanis decided to scramble jets or whatever else, they didn't know who was on those jets. They had no idea about who might have been on there, whether it be the U.S. or somebody else."

In the aftermath of the mission, Brennan said there's considerable dialogue between U.S. and Pakistani counterterrorism officials. Though Musharraf has sharply criticized the U.S. action, Brennan said officials of the current government are "expressing understanding about the reasons why we did this."

"They are appreciative that it was done without having Pakistani casualties outside of that compound," he added.

Fox News' Anne McGinn, Wendell Goler and Amy Kellogg contributed to this report.