WASHINGTON — The evacuation of 125 United States Special Operations advisers from Yemen in the past two days is the latest blow to the Obama administration’s counterterrorism campaign, which is already struggling with significant setbacks in Syria, Libya and elsewhere in the volatile region, American officials said Sunday.

The loss of Yemen as a base for American counterterrorism training, advising and intelligence-gathering carries major implications not just there, but throughout a region that officials say poses the most grievous threat to United States global interests and to the country itself.

The rapid rise of the Islamic State has commanded the immediate attention of President Obama and other Western leaders in the past year. But American officials say that Al Qaeda’s affiliate in Yemen, which includes the most potent bomb maker in the terrorist world, still poses the most direct threat to Americans at home, abroad or aboard commercial aircraft. Since 2009, the United States has thwarted at least three plots by the group to bring down airliners.

Even after the withdrawal of American troops, the Central Intelligence Agency will still maintain some covert Yemeni agents in the country. Armed drones will carry out some airstrikes from bases in nearby Saudi Arabia or Djibouti in the Horn of Africa, as was done most recently on Feb. 20. Spy satellites will still lurk overhead and eavesdropping planes will try to suck up electronic communications.