Washington (CNN) -- The United States is watching closely to the see the ultimate fate of the most powerful man in Pakistan, Gen. Ashfaq Parvez Kayani, the Pakistani army's chief of staff.
Pressured by Washington to crack down on terrorists at the same time he was kept in the dark about the U.S. raid to kill Osama bin Laden, Kayani "is facing more vocal and strident criticism than he has in the past," a senior U.S. military official told CNN. "We really think he is coming under increased scrutiny by junior and mid-grade officers."
This is the type of scrutiny senior Pakistani generals like Kayani are "not accustomed to facing," the official said.
Criticism of Kayani inside Pakistan had grown in recent months as he became close to the Obama administration and the Pentagon. But in the wake of the U.S. military raid into Pakistan to kill bin Laden, the criticism has increased from an officer corps furious that U.S. troops invaded Pakistan's territory without the Pakistani military, and especially Kayani, being consulted.
Adm. Michael Mullen, chairman of the U.S. Joint Chiefs of Staff, is one of Kayani's closest professional and personal allies, having met with him many times in the past several years.
"Mullen does consider him a friend," said the admiral's spokesman, Capt John Kirby. "That doesn't mean there aren't still disagreements. It doesn't mean Kayani doesn't feel betrayed."
U.S. officials are closely watching a group known as the "11 corps commanders," the senior Pakistani generals hand-picked by Kayani to command. Keeping their loyalty will be crucial for Kayani to keep his job.
At his final Pentagon news conference Thursday before stepping down at the end of the month, Gates warned that no matter how much strain exists between the two countries, cooperation must be preserved.
"We need each other and we need each other more than just in the context of Afghanistan. Pakistan is an important player in terms of regional stability and in terms of central Asia, and my view is that this is a relationship that we need to keep working at it."
Incoming Defense Secretary Leon Panetta on June 9 sounded a similar warning: "This is a difficult challenge. The relationship with Pakistan is at the same time one of the most critical and yet one of the most complicated and frustrating relationships that we have."
Panetta said it is "complicated by the fact that they maintain relationships with certain terrorist groups, that they continue to not take aggressive action with regard to these safe havens, and that they're concerned about the sovereignty results and criticisms of the United States when, in fact, my view is that the terrorists in their country are probably the greatest threat to their sovereignty."
For his part, Mullen, also testifying before Congress this week, said he wouldn't "push back" on the challenge of working with Pakistan.
"Some of the criticism is more than warranted. Nobody's worked that harder than me, very frankly, with the leadership. And it's a conscious decision, I think, that we have to make. And if we walk away from it, it's my view it will be a much more dangerous place a decade from now, and we'll be back."