U.S. military teams and intelligence agencies are deeply involved in secret joint operations with Yemeni troops who in the past six weeks have killed scores of people, among them six of 15 top leaders of a regional al-Qaeda affiliate, according to senior administration officials.

Members of the Yemeni counter-terrorism force take part in a training session in Sureif, a suburb of the capital Sanaa, in 2008. US military teams and intelligence agencies are deeply involved in secret joint operations with Yemeni troops who have killed six of 15 leaders of an Al-Qaeda affiliate there, the Washington Post has reported. (AFP/File/Khaled Fazaa) The operations, approved by President Obama and begun six weeks ago, involve several dozen troops from the U.S. military's clandestine Joint Special Operations Command (JSOC), whose main mission is tracking and killing suspected terrorists. The American advisers do not take part in raids in Yemen, but help plan missions, develop tactics and provide weapons and munitions. Highly sensitive intelligence is being shared with the Yemeni forces, including electronic and video surveillance, as well as three-dimensional terrain maps and detailed analysis of the al-Qaeda network.

As part of the operations, Obama approved a Dec. 24 strike against a compound where a U.S. citizen, Anwar al-Aulaqi, was thought to be meeting with other regional al-Qaeda leaders. Although he was not the focus of the strike and was not killed, he has since been added to a shortlist of U.S. citizens specifically targeted for killing or capture by the JSOC, military officials said. The officials, like others interviewed for this article, spoke on the condition of anonymity because of the sensitivity of the operations.

The broad outlines of the U.S. involvement in Yemen have come to light in the past month, but the extent and nature of the operations have not been previously reported. The far-reaching U.S. role could prove politically challenging for Yemen's president, Ali Abdullah Saleh, who must balance his desire for American support against the possibility of a backlash by tribal, political and religious groups whose members resent what they see as U.S. interference in Yemen.

The collaboration with Yemen provides the starkest illustration to date of the Obama administration's efforts to ramp up counterterrorism operations, including in areas outside the Iraq and Afghanistan war zones.

"We are very pleased with the direction this is going," a senior administration official said of the cooperation with Yemen.

Obama has ordered a dramatic increase in the pace of CIA drone-launched missile strikes into Pakistan in an effort to kill al-Qaeda and Taliban members in the ungoverned tribal areas along the Afghan border. There have been more such strikes in the first year of Obama's administration than in the last three years under President George W. Bush, according to a military officer who tracks the attacks.

Obama also has sent U.S. military forces briefly into Somalia as part of an operation to kill Saleh Ali Nabhan, a Kenyan sought in the 2002 bombing of an Israeli-owned resort in Kenya.

Republican lawmakers and former vice president Richard B. Cheney have sought to characterize the new president as soft on terrorism after he banned the harsh interrogation methods permitted under Bush and announced his intention to close the U.S. military prison at Guantanamo Bay, Cuba.

Obama has rejected those two elements of Bush's counterterrorism program, but he has embraced the notion that the most effective way to kill or capture members of al-Qaeda and its affiliates is to work closely with foreign partners, including those that have feeble democracies, shoddy human rights records and weak accountability over the vast sums of money Washington is giving them to win their continued participation in these efforts.

In the case of Yemen, a steady stream of high-ranking officials has visited Saleh, including the rarely seen JSOC commander, Vice Adm. William H. McRaven; White House counterterrorism adviser John O. Brennan; and Gen. David H. Petraeus, head of U.S. Central Command.

A Yemeni official briefed on security matters said Tuesday that the two countries maintained a "steadfast cooperation in combating AQAP, but there are clear limits to the U.S. involvement on the ground. Information sharing has been a key in carrying out recent successful counterterrorism operations." AQAP is the abbreviation for al-Qaeda in the Arabian Peninsula, the affiliate operating in Yemen.

In a newly built joint operations center, the American advisers are acting as intermediaries between the Yemeni forces and hundreds of U.S. military and intelligence officers working in Washington, Virginia and Tampa and at Fort Meade, Md., to collect, analyze and route intelligence.

The combined efforts have resulted in more than two dozen ground raids and airstrikes. Military and intelligence officials suspect there are several hundred members of AQAP, a group that has historical links to the main al-Qaeda organization but that is thought to operate independently.

The chairman of the Joint Chiefs of Staff, Adm. Mike Mullen, told a Navy War College class in early January that the United States had "no plans" to send ground troops to Yemen and that he had been concerned about the growing al-Qaeda presence there "for a long time now."

"We have worked hard to try to improve our relationships and training, education and war-fighting support," Mullen said. "And, yet, we still have a long way to go."

Saleh has faced pressure not only from the United States but also his country's main financial backers, Saudi Arabia and the United Arab Emirates, to gain better control over its lawless northern border. In August, Saleh asked U.S. officials to begin a more in-depth conversation over how the two countries might work together, according to administration officials. The current operation evolved from those talks.

"President Saleh was serious about going after al-Qaeda and wasn't going to resist our encouragement," the senior official said.

The Obama administration's deepening of bilateral intelligence relations builds on ties forged during George J. Tenet's tenure as CIA director.

Shortly after the Sept. 11, 2001, attacks, Tenet coaxed Saleh into a partnership that would give the CIA and U.S. military units the means to attack terrorist training camps and al-Qaeda targets. Saleh agreed, in part, because he believed that his country, the ancestral home of Osama bin Laden, was next on the U.S. invasion list, according to an adviser to the Yemeni president.

Tenet provided Saleh's forces with helicopters, eavesdropping equipment and 100 Army Special Forces members to train an antiterrorism unit. He also won Saleh's approval to fly Predator drones armed with Hellfire missiles over the country. In November 2002, a CIA missile strike killed six al-Qaeda operatives driving through the desert. The target was Abu Ali al-Harithi, organizer of the 2000 attack on the USS Cole. Killed with him was a U.S. citizen, Kamal Derwish, who the CIA knew was in the car.

Word that the CIA had purposefully killed Derwish drew attention to the unconventional nature of the new conflict and to the secret legal deliberations over whether killing a U.S. citizen was legal and ethical.

After the Sept. 11 attacks, Bush gave the CIA, and later the military, authority to kill U.S. citizens abroad if strong evidence existed that an American was involved in organizing or carrying out terrorist actions against the United States or U.S. interests, military and intelligence officials said. The evidence has to meet a certain, defined threshold. The person, for instance, has to pose "a continuing and imminent threat to U.S. persons and interests," said one former intelligence official.

The Obama administration has adopted the same stance. If a U.S. citizen joins al-Qaeda, "it doesn't really change anything from the standpoint of whether we can target them," a senior administration official said. "They are then part of the enemy."

Both the CIA and the JSOC maintain lists of individuals, called "High Value Targets" and "High Value Individuals," whom they seek to kill or capture. The JSOC list includes three Americans, including Aulaqi, whose name was added late last year. As of several months ago, the CIA list included three U.S. citizens, and an intelligence official said that Aulaqi's name has now been added.

Intelligence officials say the New Mexico-born imam also has been linked to the Army psychiatrist who is accused of killing 12 soldiers and a civilian at Fort Hood, Tex., although his communications with Maj. Nidal M. Hasan were largely academic in nature. Authorities say that Aulaqi is the most important native, English-speaking al-Qaeda figure and that he was in contact with the Nigerian accused of attempting to bomb a U.S. airliner on Christmas Day.

Yemeni Foreign Minister Abubaker al-Qirbi said in Washington last week that his government's present goal is to persuade Aulaqi to surrender so he can face local criminal charges stemming from his contacts with the Fort Hood suspect. Aulaqi is being tracked by the country's security forces, the minister added, and is now thought to be in the southern province of Shabwa.

Staff writer R. Jeffrey Smith and staff researcher Julie Tate contributed to this report.