Even before the disintegration of the government, officials say, the growing chaos in Yemen had resulted in a steady erosion in intelligence-gathering efforts against AQAP and a de facto suspension in raids by Yemeni units trained, equipped and often flown to targeted al-Qaeda compounds by U.S. forces.

“The agencies we worked with . . . are really under the thumb of the Houthis. Our ability to work with them is not there,” said a senior U.S. official closely involved in monitoring the situation. In a measure of U.S. concern over the crisis, officials also signaled for the first time a willingness to open talks with Houthi leaders, despite their suspected ties to Iran and antipathy toward the United States.

The developments have unraveled a campaign that President Obama described last year as a model for how the United States should fight terrorist groups, and avoid being drawn more directly into overseas conflicts. The turmoil in Yemen has exposed the risks of that strategy, with U.S. officials now voicing concern that the suspension in operations in Yemen could enable AQAP — which has launched a series of plots against the United States and claimed credit for the attacks in Paris this month — to regroup.