The airstrikes in Yemen this year have been split fairly evenly between operations carried out by CIA Predators and those conducted by JSOC using Reapers and other drones as well as conventional aircraft. (MASSOUD HOSSAINI/AP)

There is little doubt among U.S. intelligence officials that Kaid and Nabil al-Dhahab — brothers who reportedly survived a U.S. airstrike in Yemen on Memorial Day — are associated with the al-Qaeda insurgency in that country. Less clear is the extent to which they are plotting against the United States.

“It’s still an open question,” a U.S. counterterrorism official said. The siblings were related by marriage to Anwar al-Awlaki, an al-Qaeda operative killed in September, but they have not been connectedto a major plot. Their focus has been “more local,” the official said. But “look at their associations and what that portends.”

The quickening pace of the U.S. drone campaign in Yemen this year has raised new questions about who is being targeted and why. A review of strikes there so far suggests that the Obama administration has embraced a broader definition of what constitutes a terrorism threat that warrants a lethal response.

In more than 20 U.S. airstrikes over a span of five months, three “high-value” terrorism targets have been killed, U.S. officials said. A growing number of attacks have been aimed at lower-level figures who are suspected of having links to terrorism operatives but are seen mainly as leaders of factions focused on gaining territory in Yemen’s internal struggle.

News accounts from inside the country — which vary in their reliability — also suggest that U.S. airstrikes have hit military targets, including a weapons storage facility near Jaar, a city in southern Yemen. In some cases, U.S. strikes appeared to be coordinated with Yemeni military advances on al-Qaeda positions in the southern provinces of Abyan and Shabwa.

U.S. drone strikes on rise in Yemen (The Washington Post/The Long War Journal)

Current and former U.S. officials familiar with the campaign said restrictions on targeting have been eased amid concern over al-Qaeda’s expansion over the past year. Targets still have to pose a “direct threat” to U.S. interests, said a former high-ranking U.S. counterterrorism official. “But the elasticity of that has grown over time.”

The adjustments in the drone campaign carry risks for the Obama administration, which had sought to minimize the number of strikes out of fears of radicalizing local militants and driving them into al-Qaeda’s ranks. Growing unrest in Yemen has blurred the boundaries between al-Qaeda cells plotting terrorist attacks and a broader insurgency that operates under the terrorist network’s brand.

A White House spokesman said the U.S. mission in Yemen remains narrow.

“We’re pursuing a focused counterterrorism campaign in Yemen designed to prevent and deter terrorist plots that directly threaten U.S. interests at home and abroad,” said Tommy Vietor, spokesman for the National Security Council. “We have not and will not get involved in a broader counterinsurgency effort.”

But other U.S. officials said that the administration’s emphasis on threats to interests “abroad” has provided latitude for expanding attacks on al-Qaeda in the Arabian Peninsula (AQAP), as the Yemen affiliate is known.

In early May, a U.S. attack killed an operative, Fahd al-Quso, tied to the latest AQAP plot to smuggle explosives-laden underwear onto a flight to the United States. But officials said the campaign is now also aimed at wiping out a layer of lower-ranking operatives through strikes that can be justified because of threats they pose to the mix of U.S. Embassy workers, military trainers, intelligence operatives and contractors scattered across Yemen.

Asked about the reported March 12 attack on the weapons site, a U.S. military official said, “That sounds like a counterterrorism target.”

That official, and others, spoke on the condition of anonymity, citing the sensitive nature of U.S. operations in Yemen. Spokesmen for the CIA and Pentagon declined to comment.

One of the U.S. objectives in Yemen has been “identifying who those leaders were in those districts that were al-Qaeda and also in charge of the rebellion,” said a former senior U.S. official who was involved in overseeing the campaign before leaving the government. “There was a little liberalization that went on in the kill lists that allowed us to go after them.”

The nerve center of those operations is a joint targeting cell on the outskirts of Sanaa, the capital. Inside, teams from Yemen’s special forces and the U.S. Joint Special Operations Command (JSOC) comb through intelligence to identify targets and coordinate which side should carry out strikes.

The effort nearly ground to a halt last year amid a political crisis that finally forced Yemen’s leader for three decades, Ali Abdullah Saleh, to step down. As he fought to cling to power, U.S. officials said they became concerned that he was trying to direct U.S. strikes against his adversaries under the guise of providing locations of supposed terrorist groups.

“There were times when we were intentionally misled, presumably by Saleh, to get rid of people he wanted to get rid of,” said the former U.S. official involved in overseeing the campaign.

Since Saleh was replaced by Abd Rabbuh Mansur al-Hadi, the targeting work has resumed, and U.S. military advisers who had been pulled out of the country have returned.

U.S. officials said the U.S. presence in Yemen has included members of SEAL Team 6, the unit used in the Osama bin Laden raid. The rules of engagement allow U.S. special operations forces to get no closer to the enemy than the “last position of cover,” meaning the final staging areas from which Yemeni units mount assaults.

The airstrikes in Yemen this year have been split fairly evenly between operations carried out by CIA Predators and those conducted by JSOC using Reapers and other drones as well as conventional aircraft, U.S. officials said.

The CIA had pushed for an expansion of the targeting rules in Yemen, seeking to replicate aspects of its drone campaign against al-Qaeda in Pakistan. President Obama recently authorized the agency and JSOC to carry out “signature strikes” that are based on patterns of suspicious behavior, even when the identities of those who would be killed is not clear.

According to the Long War Journal, a Web site that tracks drone activity, there have been 22 strikes so far this year in Yemen, more than in the previous 10 years combined. U.S. officials said the pace has accelerated even though there has not been a proliferation in the number of plots, or evidence of a significantly expanded migration of militants to join AQAP.

The group has been linked to a series of high-level plots, including the attempt to bomb a Detroit-bound airliner on Christmas Day in 2009.

That attack and others prompted a shift in resources to the region by the CIA, the National Security Agency and other spy services. U.S. officials said the spike in the number of drone attacks this year has been driven in part by intelligence gains and the ability to identify more targets.

The disruption of an underwear-bomb plot last month illustrated the extent to which the CIA, along with partners including the spy services of Britain and Saudi Arabia, have been able to penetrate AQAP.

But the expansion of the campaign is traced mainly to rising concern over AQAP’s territorial expansion. The group and its Ansar al-Sharia wing have seized control of cities including Jaar, potentially providing sanctuary for the planning of terrorist attacks.

The Dhahab brothers are examples of the murky overlap between the regional and transnational factions of AQAP.

Their feud-divided family had seized control of the city of Radda earlier this year. Their sister had been married to Awlaki, the U.S.-born cleric and operative who was killed in a CIA drone strike.

They are primarily seen as leaders of an al-Qaeda insurgency in Baydah province, but the U.S. counterterrorism official said there is concern that their roles have grown “possibly beyond that.”