Even in a neighborhood of roomy modern residences, the three-story white house stood out. The home, down the street from an elite Pakistani military academy, was eight times as large as others nearby. Its razor-wire-topped walls were higher. Its occupants acted mysteriously, neighbors said, burning trash rather than placing it outside.

With the Monday killing of Osama bin Laden, the mystery of who lived in the Abbottabad house was solved. And that resolution revealed that the world’s most wanted man had been living for years not only in relative comfort but also at the doorstep of Pakistan’s powerful army.

The disclosure threatened to unravel the remaining threads in a U.S.-Pakistan relationship that is severely strained by mistrust.

The scene of bin Laden’s killing immediately raised questions about how Pakistan’s powerful military, which U.S. officials have long suspected of tolerating and harboring Islamist militants, could not have known about his presence — and even whether it had provided him shelter. Bin Laden joined a long list of high-value terrorism figures captured or killed in recent years not in Pakistan’s remote tribal belt but in the sprawling urban centers in the heart of the country.

“Either we’re dealing with an extraordinarily incompetent military and army and intelligence agency, or at some level they were complicit,” said Shaun Gregory, a Pakistan scholar at the University of Bradford in England.

Abbottabad, the bucolic city just north of Islamabad where bin Laden had been hiding, has long been a refuge for tourists and a hub for Pakistan’s military, with two infantry regiments based there. Bin Laden’s home was in a neighborhood well traveled by military vehicles and full of military families.

In Washington, convictions deepened that Pakistan — which has accepted billions of dollars in military aid since allying itself with the United States in 2001 in counterterrorism efforts — was either uncommitted to the hunt for terrorists on its soil or betraying the United States by protecting them. U.S. officials have long said that bin Laden was in Pakistan, and Pakistan has long called on the United States to provide proof.

But in the end, after a decade-long hunt, it appeared that the United States did not trust Pakistan enough to do so. U.S. officials insisted that Pakistan was not told about the operation until U.S. forces had left Pakistani airspace.

Officials were cryptic about whether Pakistani intelligence had aided the operation in any way. The Pakistanis “were not aware of our interest in this compound, but they provided us information attached to it to help us complete the robust intelligence case that eventually carried the day,” said a senior U.S. intelligence official, who like other officials spoke on the condition of anonymity because of the sensitivity of the matter.

Basking in the glow of the successful operation, senior Obama administration officials tried hard to sidestep questions about possible Pakistani complicity in hiding bin Laden, while also acknowledging skepticism about Pakistan’s assertion that it had been in the dark.

“I think it’s inconceivable that bin Laden did not have a support system in [Pakistan] that allowed him to remain there for an extended period of time,” said John O. Brennan, President Obama’s top counterterrorism adviser. “I am not going to speculate about what type of support he might have had on an official basis inside Pakistan.”

On Capitol Hill, lawmakers were more pointed.

“They got a lot of explaining to do,” Sen. Carl Levin (D-Mich.) said of the Pakistanis.

Many bluntly said U.S. military and economic assistance to Pakistan is at risk. “We clearly need to keep the pressure on Pakistan, and one way to do that is to put more strings attached to the tremendous amount of military aid that we give the country,” Sen. Susan Collins (R-Maine) said at a news conference.

A Senate hearing on U.S.-Pakistan relations is scheduled for this week.

Compound in Abbottabad

A U.S. defense official briefing reporters on the mission said unequivocally, “We have no indications that the Pakistanis were aware that Osama bin Laden was at the compound in Abbottabad.”

That line was echoed by Husain Haqqani, Pakistan’s ambassador to the United States, and a senior Pakistani intelligence official, both of whom insisted that Pakistan was unaware bin Laden was living there.

Many in Pakistan, including former president Pervez Musharraf, deemed the U.S. operation a violation of the country’s sovereignty that was likely to spur more reprisal terrorist attacks against Pakistan. Others described it as profoundly embarrassing for the Pakistani military.

A U.S. official said the Obama administration was “very concerned” that bin Laden was hiding in such a well-populated part of Pakistan. “This is something that we’re going to continue to work with the Pakistani government on,” the official said.

Other terrorism figures have also been caught in Pakistani cities, far from the rugged borderlands where al-Qaeda, the Taliban and a stew pot of other militant groups are thought to hide. But bin Laden was not the first terrorism figure discovered in Abbottabad: Earlier this year, Pakistani officials said they arrested Umar Patek, an Indonesian al-Qaeda leader, in the city.

Abbottabad has attracted many refugees from recent Pakistani counterinsurgency offensives in the western tribal areas and in the Swat Valley, as well as from Afghanistan. They have made the city a linguistic and ethnic patchwork — and probably a good place to hide despite the military presence, some here said.

“People don’t really care now to ask who’s there,” said Gohar Ayub Khan, a former foreign minister from the city. “That’s one of the reasons why, possibly, he came in there.”

Worsening bilateral ties

U.S. officials have long asserted that the Afghan Taliban leadership is based in the southwestern Pakistani city of Quetta and that another lethal Afghan insurgent group, the Haqqani network, enjoys relative freedom inside Pakistan’s mountainous tribal areas thanks to its long-standing ties to Pakistani intelligence. Pakistan denies both allegations.

U.S.-Pakistan relations, long marred by suspicions, have deteriorated this year. After a CIA contractor fatally shot two Pakistanis in January, joint intelligence operations came to a standstill, and Pakistan recently demanded a scaling back of CIA operations, including drone strikes.

Other U.S. officials, meanwhile, have expressed growing frustration about Pakistan’s hesitant military fight against Islamist insurgents and its suspected ties to the Haqqani network, which is based in Pakistan but strikes U.S. troops in Afghanistan. Those comments have riled Pakistan’s army, whose chief, Gen. Ashfaq Kayani, told cadets at the military academy in Abbottabad just last week that his troops had “broken the backs” of insurgents.

Pakistani officials deflected the criticisms, saying their nation was committed to fighting terrorism. A statement from Prime Minister Yousaf Raza Gillani said it was time for “positive messaging about Pakistan rather than finger pointing.”

But a Pakistani official also said that the government’s near silence on the Abbottabad operation was indicative of a delicate balancing act in a strongly anti-American nation where a significant section of society sympathizes with jihadists. On Monday, insurgent leaders were threatening to avenge bin Laden’s death with attacks on Pakistan.

The Pakistani intelligence official said the discovery that bin Laden was living very close to Pakistani military installations was embarrassing “to an extent, yes.”

But the official denied any prior knowledge of bin Laden’s presence.

“Had we known,” the official said, “we would have taken him out.”

DeYoung reported from Washington. Special correspondents Shaiq Hussain in Islamabad and Haq Nawaz Khan in Abbottabad contributed to this report.