WASHINGTON - A surveillance aircraft operated by the U.S. Joint Special Operations Command flew over southeast Yemen on the evening of March 9, tracking a mid-level al-Qaida commander as he drove to his mountain hideout.

American missiles soon rained down. The al-Qaida commander was killed, along with 22 other suspected militants, most of them believed to be young recruits receiving military training, U.S. officials said.

The attack is an example of how the U.S. is escalating its largely secret campaign in Yemen, taking advantage of improved intelligence and of changes in Yemen's leadership now that President Ali Abdullah Saleh has stepped down. The changes have allowed attacks against militants who until recently might have eluded U.S. attention, the officials say.

As the pace quickens and the targets expand, however, the distinction may be blurring between operations targeting militants who want to attack Americans and those aimed at fighters seeking to overthrow the Yemeni government.

U.S. officials insist that they will not be drawn into a civil war and that they do not intend to put ground troops in Yemen other than trainers and small special operations units.

"We don't want to become involved in the country's internal battles," an Obama administration official said. "We don't want to turn every anti-government fighter against the United States."

The U.S. has focused its airstrikes in areas where militants from al-Qaida in the Arabian Peninsula, the main insurgent group operating in Yemen, and their tribal allies have seized and held towns in the last year.

The stepped-up U.S. attacks appear aimed in part at preventing militants from consolidating control over the region - the southern Yemen provinces of Abyan, Shabwa and Bayda. Parts of those provinces have become the world's largest haven for al-Qaida in the years since the U.S. began drone strikes in the tribal areas of Pakistan, U.S. officials say.

Most militants fighting under the al-Qaida banner in Yemen are local insurgents, U.S. officials say, along with Saudis bolstering the ranks and assuming leadership roles. Some of the militants are known to harbor ambitions of attacking the West: Ibrahim Hassan Asiri, who made the underwear bomb used by Umar Farouk Abdulmutallab in an attempt to blow up an airliner over Detroit, remains at large in Yemen, U.S. officials say.

The militants say they are fighting the governments in Sana and Riyadh as well as the United States. They have mounted lethal attacks on Yemeni government officials and civilians, including a March 5 battle that killed 100 Yemeni soldiers. An al-Qaida affiliate claimed credit for a March 18 attack in which an American teacher was shot and killed by motorcycle-riding assailants.

The U.S. effort in Yemen was brought to a virtual standstill - a "lull," Gen. James N. Mattis told Congress - by Saleh's yearlong effort to cling to power. The U.S. did not want to be seen as backing a repressive ruler, and it also became dangerous for American personnel to be in the country. Since Saleh's departure, the use of drones and manned warplanes to attack militants has expanded significantly.

In the last few weeks, an airstrike killed three fighters in the town of Jaar on March 11, then three days later an American missile hit a vehicle and killed four militants in Bayda. U.S. officials said both attacks were carried out either by the military's U.S. Joint Special Operations Command or the CIA, each of which fly armed drones over Yemen.

The militants were targeted not because they were plotting attacks against the U.S. but because intelligence suggested they were planning attacks on American diplomats or other targets inside Yemen, the U.S officials said.

The CIA began flying drones over Yemen last year, joining a clandestine military program that was already up and running. Some military drones fly from a base in Djibouti, and CIA drones are based at an undisclosed location in the Arabian Peninsula.

U.S. officials would not say exactly how many strikes have been carried out in Yemen, and it's sometimes difficult to distinguish between Yemeni military attacks and American actions. Long War Journal, a website that tracks U.S. counterterrorism actions, estimates that 23 strikes have been carried out in Yemen since January 2009, far lower than the 245 drone strikes it counted in Pakistan during that period.

Since 2002, 160 militants and 47 civilians were killed in drone strikes in Yemen, the website found. That is a much higher rate of civilian deaths than independent experts have seen in the U.S. drone war in Pakistan.

Several officials said there are high-level discussions in Washington about ways to further expand the U.S. role. U.S. and Yemeni officials have been surprised and dismayed by how easily al-Qaida militants have been able to seize and hold territory in parts of Yemen, and they are determined to reverse the gains, they say.

The militants in Yemen "are under pressure, but the fact that there are these areas where they can now operate with relative impunity is of deep concern," a senior U.S. official said.

Yemen's new president, Abdu Rabu Mansour Hadi, has proved more willing than his predecessor to approve U.S. airstrikes, one of the reasons for the recent surge in attacks, American and Yemeni officials said.

Last week, Yemen's army chief of staff, Maj. Gen. Ahmed Ali Ashwal, was in Washington for talks with Pentagon officials. The U.S. is pushing Yemen to reorganize its military so that it is better positioned to retake the towns now held by al-Qaida, an effort that will require tanks and other heavy weapons, U.S. officials said.

Washington is pressing Hadi to get rid of several of Saleh's relatives who remain in key military and security posts and to mount a serious military campaign to retake territory in the south.

Hadi "has shown the will and ability to make the changes. ... It's a matter of getting the right focus and the right plan and someone to lead it," the senior Defense official said.

Heavily armed American soldiers have begun appearing in large numbers at the Sheraton Hotel in the capital, Sana, a Yemeni official said.

Obama administration officials insist that the rules for targeting al-Qaida militants in Yemen have not changed.

In an example of the limits, U.S. forces in Yemen have not used so-called signature strikes that have been employed in Pakistan - in which the CIA has used drones to kill fighters on the basis of observed activities that suggested they were insurgents. Targeting in Yemen is based on intelligence about particular people, not "pattern of life" analysis, they say.

Some Obama administration officials and members of Congress favor signature strikes in Yemen, but President Barack Obama has resisted, officials say.

One reason for concern about the U.S. strikes is that the intelligence hasn't always been good enough for U.S. commanders to be sure what their missiles were aimed at, officials said.

In March 2010, a strike killed the deputy governor of Marib as he sat for negotiations with an al-Qaida leader. Afterward, U.S. officials "said we're not doing drones because we don't have the intelligence structure to be able to do it well," said Barbara Bodine, who was U.S. ambassador to Yemen from 1997 to 2001.

When the drone strikes resumed, the vetting was rigorous, officials say. Even so, the new, more aggressive approach troubles some critics, who argue that U.S. military strikes have done more harm than good.

"The more the U.S. applies its current policy, the stronger al-Qaida seems to get," said Charles Schmitz, a Yemen expert at Towson University.

Some analysts argue the American military effort has provoked widespread anger among Yemenis.

"Drones are a weapon of terror in many ways, and the kind of hostility this is going to breed may not be worth the counterterrorism gains," Bodine said.