ISLAMABAD, Pakistan - The CIA yanked its top spy out of Pakistan after his cover was blown and his life threatened, and 54 suspected extremists were killed in a U.S. drone missile attack Friday in stark new signs of the troubled relationship between mistrustful allies locked in a war on terror groups.

The CIA's decision to remove its Islamabad station chief comes at a pivotal moment. The Obama administration is stepping up its pressure on Pakistan to rid its lawless northwest frontier of extremists, even as public outcry in the country has intensified against the U.S. spy agency's unacknowledged drone war that has killed dozens of civilians.

The outing of the station chief has spurred questions about whether Pakistan's spy service might have leaked the information. The name emerged publicly from a Pakistani man who has threatened to sue the CIA over the deaths of his son and brother in a 2009 drone missile strike. A lawsuit filed last month in New York City in connection with the 2008 attacks in Mumbai, India, also may have raised tensions by naming Pakistan's intelligence chief as a defendant.

A Pakistani intelligence officer said the country's intelligence service knew the identity of the station chief but had "no clue" how the name was leaked. The officer spoke on condition of anonymity because his agency, like many around the world, does not allow its operatives to be named in the media.

CIA air strikes in Pakistan from unmanned aircraft have eliminated extremist leaders but also have led to accusations that the strikes kill innocent civilians. The United States does not acknowledge the missile attacks, but there have been more than 110 this year - more than double last year's total.

The 54 suspected extremists killed Friday died in three American drone attacks close to the Afghan border. The high death toll included commanders of a Taliban-affiliated group who were holding a meeting when the missiles struck.

Drone strikes were at issue in November, when a Pakistani man, Kareem Khan, held a news conference, saying they would seek a $500 million payment in two weeks for the deaths of Khan's son and brother, or they would sue CIA Director Leon E. Panetta, U.S. Defense Secretary Robert M. Gates and the man they identified as the CIA station chief in Islamabad. The Pakistanis said they would sue for "wrongful death" in a Pakistani court, but the lawsuit has yet to be filed.

Last week, Khan filed a complaint with the police, asking them to investigate the CIA station chief in the deaths of his brother and son.

Although the lawsuit gave an American name for the station chief, the name was not listed correctly in those documents. The AP is not publishing the station chief's name because he remains undercover and his identity is classified.

The CIA did not immediately move to pull the station chief out after the lawsuit was threatened. It wasn't until the man, who had previously served in Baghdad, began receiving death threats that the agency acted. The station chief had been due to return to the United States in January.

"Our station chiefs routinely encounter major risks as they work to keep America safe, and they've been targeted by terrorists in the past," CIA spokesman George Little said Friday. "They are courageous in the face of danger, and their security is obviously a top priority for the CIA."

A U.S. intelligence official said Friday that the recall of the station chief would not hinder agency operations in Pakistan.

The CIA's work is unusually difficult in Pakistan, one of the United States' most important and at times frustrating counterterrorism allies. The station chief in Islamabad operates as a virtual military commander in the U.S. war against al-Qaeda and other extremist groups hidden along the Pakistan-Afghanistan border.

The chief runs the Predator drone program targeting extremists and handles some of the CIA's most urgent and sensitive tips.

The station chief also collaborates closely with Pakistan's Inter-Service Intelligence, or ISI, in a relationship that has been as contentious as it has been useful in recent years. The alliance has led to strikes on key extremist leaders but has also been marred by sharp disagreements between the two agencies.

During the first term of President George W. Bush's administration, Pakistan almost expelled a previous CIA station chief in a dispute about sharing intelligence.

The civil lawsuit filed in Brooklyn federal court last month also has raised tensions. The suit accused Pakistan's ISI spy service of nurturing extremists involved in the 2008 Mumbai attacks. The suit listed Gen. Ahmed Shuja Pasha, head of the ISI, as a defendant.

In the case in Pakistan, lawyer Shahzad Akbar said he got the station chief's identity from local journalists. He said he included the name in the lawsuit because he wanted to sue a CIA operative living within the jurisdiction of the Islamabad court.

"He was facing legal charges," Akbar said. "It would have been embarrassing for the U.S. They were worried about being asked pertinent questions about CIA operations in Pakistan."

It is rare for a CIA station chief to be pulled out because of a blown cover. In 1999, an Israeli newspaper revealed the identity of the station chief in Tel Aviv. In 2001, an Argentine newspaper printed a picture of the Buenos Aires station chief and details about him. In both instances, the station chiefs were recalled.

The AP learned about the station chief's removal Thursday but held the story until he was out of the region.

The drone attacks Friday took place in the Khyber tribal region, an area rarely targeted by U.S. missiles over the last three years. That indicates an expansion of the CIA-led covert campaign of drone strikes inside Pakistan.

Most of the more than 100 missile attacks this year inside Pakistan have taken place in North Waziristan, which is effectively under the control of a mix of Taliban, al-Qaeda, and related groups. The region, seen as the major extremist sanctuary in Pakistan, has yet to see an offensive by the Pakistani military.

During Thursday's review of the Afghan war, President Obama urged Pakistan to do more in defeating extremists in the border lands.