U.S. spy agencies have gathered new intelligence indicating that al-Qaeda’s affiliate in Yemen may be close to launching a terrorist strike, according to U.S. officials who said the development has added new urgency to concerns about the turmoil in the Middle East.

The officials said the agencies have assembled only fragmentary information on the plot and do not have enough detail to issue a public warning or to take specific measures to counter the threat.

But officials said the intelligence is regarded as credible, creating a scenario that has worried U.S. counterterrorism officials since the crisis in the Middle East began. The threat comes at a time when counterterrorism operations in Yemen have been disrupted by mass protests that threaten the 32-year rule of President Ali Abdullah Saleh.

The new information goes beyond the routine level of terrorism chatter monitored by U.S. spy agencies tracking al-Qaeda in the Arabian Peninsula (AQAP), as the Yemen-based offshoot is known. A U.S. official described the recent intelligence as pointing to “a current and concerning threat.”

“We’re always at a very high level of alert and have been for some time with AQAP,” said the official, speaking on the condition of anonymity to discuss an intelligence matter. But the new information points to “more than that they are bent on attacking the West and continuing to plot.”

The information has been communicated to senior officials and lawmakers in briefings, and circulated within the U.S. intelligence community, in recent days. A prominent concern, officials said, is that efforts to unravel the plot could be complicated by the political upheaval sweeping much of the Middle East.

Over the past 18 months, the United States has deployed dozens of CIA operatives and U.S. Special Operations troops to work alongside Yemeni forces in pursuing AQAP.

Last year, the United States also began patrolling above Yemen with armed Predator drones. But after a flurry of missile attacks against AQAP targets in late 2009 and early 2010, there have been no such strikes, as members of the terrorist group have burrowed into tribal enclaves in Yemen’s rugged terrain.

AQAP has carried out small-scale attacks in Yemen in recent weeks, including the fatal shooting of six soldiers in the provinces of Marib and Abyan.

Meanwhile, the survival of Saleh’s government is in doubt. This week the country’s most powerful military officer broke ranks with the government and ordered his troops to protect protesters flooding the streets of the capital, Sanaa.

Saudi Arabia’s attention has also been diverted from counterterrorism efforts. The monarchy recently dispatched forces to help subdue a popular uprising in the neighboring Sunni-dominated country of Bahrain.

In response to questions about the new threat, National Security Council spokesman Tommy Vietor said, “We continue to take very seriously the threat posed by AQAP. . . . They are the most active AQ franchise, and we are working diligently with our partners to disrupt their activities.”

Officials with the National Counterterrorism Center and the Department of Homeland Security declined to comment.

In congressional testimony last month, Michael Leiter, director of the counterterrorism center, described AQAP as “probably the most significant risk to the U.S. homeland.”

That is in part because of the expanding role of Anwar al-Aulaqi, an American-born cleric seen as having increasingly direct involvement in orchestrating AQAP attacks.

Aulaqi, 39, has a wide online following for his English-language sermons and has been linked to the 2009 shootings at Fort Hood, Tex., and the attempted bombing, seven weeks later, of a Detroit-bound airliner on Christmas Day.

U.S. officials have also cited other factors in AQAP’s emergence, including its willingness to use sophisticated explosives against what it perceives as soft targets.

Earlier this week, the State Department announced that it had designated AQAP’s main bombmaker, Ibrahim Hassan al-Asiri, as a terrorist and that the U.S. government was taking steps to seize or block money supporting him.

Asiri is believed to have designed the bomb that a Ni­ger­ian hid in his underwear during the attempted bombing of the Detroit-bound plane, as well as the explosive devices hidden inside printer cartridges that were mailed to American addresses as part of last year’s parcel-bomb plot.

Staff writer Karen DeYoung contributed to this report.