The findings released Wednesday by U.S. intelligence officials cast doubt on the longstanding suspicions by many people who reported cases that Russia or another country may have been running a global campaign to harass or attack Americans using some form of directed energy.

Instead, officials say, there is more evidence that foreign countries were not involved. In some cases, the U.S. detected among adversarial governments confusion about the allegations and suspicions that Havana syndrome was an American plot.

Two officials familiar with the assessment briefed reporters Wednesday on condition of anonymity, under ground rules set by the U.S. Director of National Intelligence.

Investigators reviewed roughly 1,500 cases in 96 countries. Many of those cases, officials said, have been linked to other potential explanations aside from a foreign campaign: medical illnesses, malfunctioning air conditioning and ventilation systems, or electromagnetic waves coming from benign devices like a computer mouse.

A core group of roughly two dozen cases identified in an interim assessment published last year has been exhaustively studied, officials said. None of the cases was linked to an attack by an adversary.

Investigators also found “no credible evidence” that any adversary had obtained a weapon that could cause the reported symptoms or a listening device that might inadvertently injure people.

Havana syndrome cases date to a series of reported brain injuries in 2016 at the U.S. Embassy in Cuba. Incidents have been reported by diplomats, intelligence officers and military personnel in the Washington area and at global postings. Russia has long been suspected by some intelligence officers of using directed energy devices to attack U.S. personnel.

But the CIA last year said it believed it was unlikely that Russia or another foreign adversary had used microwaves or other forms of directed energy to attack American officials. The agency’s criticism from those who have reported cases and from advocates who accuse the government of long dismissing the array of ailments.

Democrats and Republicans also have pressed the Biden administration to determine who and what might be responsible and to improve treatment for victims. President Joe Biden last year signed a bill intended to provide better medical care. The State Department also appointed a new coordinator for its review into cases after victims criticized the previous coordinator.

Even with the lack of answers and attributions of responsibility, officials have sought to stress their commitment to victims’ health.

“I want to be absolutely clear: these findings do not call into question the experiences and real health issues that U.S. government personnel and their family members — including CIA’s own officers — have reported while serving our country,” said CIA Director William Burns in a statement. “We will continue to remain alert to any risks to the health and wellbeing of Agency officers, to ensure access to care, and to provide officers the compassion and respect they deserve.”