Al-Qaida's increased strength at organizing and training new recruits in Yemen's vast ungoverned spaces has also led the U.S. to consider boosting financial aid and sales of military equipment to Yemen's government.
Shari Villarosa, senior State Department counterterrorism adviser, said that the security situation in Yemen has "deteriorated significantly" and that the Yemeni government's political will to battle al-Qaida and other terrorist organizations has shifted at times.
"The U.S. wants to help Yemen because we do not want to see Yemen become another Afghanistan where al-Qaida can train, plan and execute terrorist actions against us," Villarosa said.
About a week after U.S. Gen. David Petraeus, the top U.S. commander in the Middle East, met with Yemeni President Ali Abdullah Saleh late last month, Yemeni forces launched anti-terrorist operations in a tribal area known as an al-Qaida safe haven.
But that operation was short-lived, as Yemeni forces were diverted days later in a protracted fight against Shiite rebels in the north - a battle that continues to escalate.
U.S. officials said that in recent visits to Yemen, American authorities expressed frustration to Yemeni leaders about the sporadic attention paid to al-Qaida militants within their borders. The officials said the Yemenis acknowledged U.S. concerns, but remain preoccupied with the northern rebels and a secessionist threat in the south.
Al-Qaida's operatives in Yemen and Saudi Arabia merged early this year to become al-Qaida in the Arabian Peninsula, or AQAP, a move that U.S. intelligence officials said was followed by more recruiting and efforts by those operatives - mostly unsuccessful - to cross the border from Yemen into Saudi Arabia.
AQAP has also made it clear in communications through the Internet and by other means that it intends to target Western interests across the Arabian peninsula.
Yemen, the ancestral homeland of Osama bin Laden, was the site of the 2000 bombing of the USS Cole, which killed 17 American sailors. There have also been a spate of assaults on the U.S. Embassy in San'a, including a 2008 bombing that killed 10 Yemeni guards and four civilians.
Defense and counterterrorism officials, who spoke on condition of anonymity to discuss intelligence reports, said they have seen evidence of lower-level al-Qaida operatives moving into Yemen from the Afghanistan-Pakistan border.
Just a few months ago, an audio message, reportedly from al-Qaida leader Naser Abdel Karim al-Wahishi, urged Yemeni citizens to unite and fight the government. A former close aide to Osama bin Laden, al-Wahishi escaped from a Yemeni prison in 2006, and has emerged as a leader of AQAP.
After al-Qaida was largely defeated by Yemeni forces in 2003, the terror group was able to rebound as the government turned its focus to flare-ups by insurgents in the north and south.
"Al-Qaida in Yemen is stronger now than it has ever been in the past," said Gregory D. Johnsen, a Yemen scholar. "The organization is attracting more recruits than ever before and it is growing increasingly more skilled at utilizing its members."
Johnsen blamed al-Qaida's re-emergence in part on failures by the U.S. and its allies to support the rickety Yemeni government and maintain a consistent level of effort against the insurgents there.
But U.S. officials caution that the movement of al-Qaida foot soldiers into Yemen has not yet been followed by a similar movement of al-Qaida leadership from the Pakistan border. There is also no indication that terror activities elsewhere in the region are being directed from Yemen - concerns that would heighten U.S. fears.
American lawmakers who recently visited Yemen said they are concerned that U.S. alarms about al-Qaida penetration have not motivated Yemen's government.
"There is no doubt in my mind that the (Yemeni) president's chief concern is preserving his power," said Sen. Susan Collins, R-Maine. "That is worrisome because al-Qaida is also a threat to his regime."
Collins met with Saleh during a visit to Yemen last week by a small Senate delegation led by Sen. John McCain, R-Ariz. The lawmakers urged Yemeni officials to improve their cooperation with the U.S., particularly with intelligence sharing on militant activities in the country.
Villarosa said the U.S. would like to see Yemen pass stronger terror financing legislation in order to prosecute those funding militant activities. At the same time, she said, Yemen must improve its own border security.
In one recent meeting with U.S. authorities, Yemeni officials pressed for a broad range of economic aid and military equipment, including trucks, helicopters and other armored vehicles. They also asked for communications devices and naval vessels to counter the surge in piracy off Yemen's shores.
The main issue for the U.S., Collins said, "is whether that equipment is going to be used in the fight against (other) insurgents or whether its going to be focused on al-Qaida, which we view as the greater threat."
A complicating issue in the U.S.-Yemeni negotiations is the American effort to return some 100 Yemenis who are currently being held at the Guantanamo Bay detention center in Cuba.
The U.S. does not want to release the detainees straight back to Yemen for fear they will simply go free. But a U.S. proposal to have the detainees first undergo a rehabilitation program in Saudi Arabia has stalled.
Collins said the recently returned delegation plans to take up the Yemen issue with Secretary of State Hillary Rodham Clinton and other officials.
"If there is better intelligence sharing and more cooperation, I for one am willing to provide more economic assistance to Yemen," Collins said.
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