A senior CIA officer who played a leading role in the hunt for Osama bin Laden will head a task force investigating the cause of mysterious, debilitating illnesses that have plagued dozens of agency personnel and other U.S. government personnel, according to current and former officials familiar with the matter.

CIA Director William J. Burns handpicked the officer, who is undercover and a veteran of counterterrorism and counternarcotics operations, these people said, speaking like others on the condition of anonymity to discuss the sensitive assignment. They added that the officer’s work on the operation to find and kill bin Laden, which the CIA counts among its historic successes, underscored the emphasis and urgency Burns placed on attributing the cause of the illnesses, which have caused headaches, hearing loss and brain injuries and led to early retirements in some instances.

“Director Burns is personally engaged with personnel affected by anomalous health incidents and is highly committed to their care and to determining the cause of these incidents,” a CIA spokesperson said.

The agency has reached no firm conclusion on what or possibly who is behind the illnesses, which have been dubbed “Havana Syndrome” because the first symptoms were reported by diplomats at the U.S. Embassy in Havana in 2016. The State Department acknowledged last week that it was investigating complaints of similar ailments reported recently by American personnel in Vienna.

The Wall Street Journal first reported the CIA officer’s appointment to lead the task force.

Burns has met privately with several officers who believe they were injured and has told them their care is a priority. He has also visited Walter Reed National Military Medical Center, where some of the ill are receiving specialized medical treatment and have been diagnosed with brain injuries.

“It is clear that Director Burns has made this issue a top priority, a sea change from the last leadership team,” said Marc Polymeropoulos, a former senior CIA officer who retired while suffering symptoms, including painful headaches, after a trip to Moscow in 2017, when he was helping run clandestine operations in Russia.

“This is critical both for the victims who are receiving health care, as well as the need to find attribution, to hold accountable those who are behind the attacks,” he added.

Several current and former officials have said they believe Russia is likely to blame for the injuries, though studies undertaken to date have failed to definitively identify the cause. The Russian government has denied any involvement in the matter.

Polymeropoulos is among the agency veterans who are critical of the previous director, Gina Haspel, for what they described as a weak and insufficient response to the ailments.

Haspel did not immediately respond to a request for comment.

Current and former intelligence officials who suspect Russia is responsible speculated that the illnesses may have been caused by technology such as microwaves or other forms of directed energy. They acknowledge a paucity of scientific data to prove that claim but point to strong circumstantial evidence: Some of the personnel got sick when they were in Russia, and Russian intelligence — specifically the GRU, its military intelligence service — has been linked to other aggressive, sometimes flamboyant attacks on American personnel overseas.

The Democratic and Republican leaders of the Senate Intelligence Committee have publicly stated they would work with the CIA “to better understand the technology behind the weapon responsible for these attacks,” leaving little doubt that top lawmakers feel the evidence points to someone deliberately inflicting injury.

“For nearly five years, we have been aware of reports of mysterious attacks on United States Government personnel in Havana and around the world,” Sens. Mark R. Warner (D-Va.) and Marco Rubio (R-Fla.) said in a statement in April. “This pattern of attacking our fellow citizens serving our government appears to be increasing.”

Burns, a former U.S. ambassador to Russia, has also indicated that he believes the injuries were inflicted deliberately.

At his confirmation hearing in February, Burns said that as director he would “make it an extraordinarily high priority to get to the bottom of who’s responsible for the attacks.”

While some intelligence officials believe Russia is responsible, they also think Cuba bears responsibility. One official said privately that it defied belief that the Cuban government would be unaware of a Foreign Service using a weapon on American personnel within its own borders. The Cuban government had denied any involvement in the matter.

Members of Congress were last briefed on the issue in April and were troubled by the lack of answers, according to people familiar with the matter.

Some officials have attributed a recent rise in possible cases to the fact that more personnel are coming forward, in the wake of Burns elevating the illnesses and, in the eyes of some, destigmatizing it.

For now, lawmakers have no plans to mount their own investigation and plan to continue monitoring the CIA’s response, according to people familiar with the matter.

Karoun Demirjian contributed to this report.