The Central Intelligence Agency (CIA) on Thursday ruled out Russia or any other foreign power's involvement in causing the mysterious illness known as Havana Syndrome.

A senior CIA official said the interim findings of the CIA investigation found that most cases could probably be connected to pre-existing medical conditions, environmental factors, or stress, The Guardian reported.

Another CIA official told USA Today that while the report is technically categorized as an interim assessment, it is a definitive and official agency finding.

The official noted that the report was based on months of intensive investigation into what was widely believed a campaign of attacks by a foreign power against U.S. spies and diplomats.

"Despite extensive investigation, we have so far not found evidence of state-actor involvement in any [Havana Syndrome] incident," the unnamed official said.

The official further noted that based on the agency's investigation, it is "unlikely" that a foreign actor such as Russia is conducting a "worldwide campaign" in harming U.S. personnel using a weapon or mechanism.

However, the official said they are not ruling out the "involvement" of a foreign actor in a small number of Havana Syndrome cases whose cause could not be determined. The official noted that the CIA task force would continue investigating these cases.

"There is a subset of cases, some of our toughest cases, that remain unresolved... We will continue an intensive effort to resolve them," the CIA official said.

READ NEXT: Secretary of State Antony Blinken Says the U.S. Still Figuring Out 'Havana Syndrome' as More Officials Get Stricken With Condition

CIA Director Pledges Continues Investigation on Havana Syndrome

In a statement, CIA Director William Burns said that although the agency reached "some significant interim findings," they were still not done investigating these Havana syndrome incidents. While underlying causes may differ, Burns noted that U.S. personnel were suffering "real symptoms." 

"We will continue the mission to investigate these incidents and provide access to world-class care for those who need it... Our commitment to care is unwavering," Burns said.

It can be recalled that Burns, who started serving as CIA director in March last year, tripled the number of medical experts working on the incidents linked to Havana Syndrome.

Senator Mark Warner, chairman of the Senate Intelligence Committee, has lauded Burns' effort, saying that he and the CIA made Havana Syndrome a "top priority" for the agency.

Warner also commented on the interim finding of the agency, pledging to work with other agencies to get to the bottom of the syndrome.

"It's important to note that today's assessment, while rigorously conducted, reflects only the interim work of the CIA task force... The Senate Intelligence Committee will continue pressing for answers on a bipartisan basis," Warner said.

Havana Syndrome Victims Support Group Slams CIA Findings

Criticisms about the CIA's findings also surfaced. In a statement, a group representing U.S. officials who have reported suspected Havana syndrome incidents ripped the CIA over its report.

"The CIA's newly issued report may be labeled 'interim' and it may leave open the door for some alternative explanation in some cases, but to scores of dedicated public servants, their families, and their colleagues, it has a ring of finality and repudiation," the group Advocacy for Victims of Havana Syndrome said.

The group further noted that they have reason to believe the CIA interim report does not even represent the consensus of the entire agency and only reflects the views of some officials "most interested in resolution and closure."

Mark Zed, a lawyer who represents 15 individuals impacted by Havana Syndrome, also slammed the findings calling it "insulting" for those who have experienced the disease.

"This report was not coordinated with other federal agencies engaged in investigating the issue... it demonstrated that the failure of the government to produce a uniform, expert report," Zed noted.

Meanwhile, U.S. Secretary of State Antony Blinken said that investigations would continue.

"We are going to continue to do everything we can, with all the resources we can bring to understand, again, what happened, why, and who might be responsible... And we are leaving no stone unturned," Blinken noted.

Havana Syndrome causes patients to experience hearing strange sounds, loss of balance, dizziness, nausea, and memory loss. Since the original outbreak of the symptoms, more than 1,000 cases have been reported and studied worldwide. Many of the cases originated at the U.S. Embassy in Havana, Cuba, beginning in 2016.

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This article is owned by Latin Post.

Written by: Joshua Summers

WATCH: Fighting An Invisible Enemy: The Voices Of Havana Syndrome - From NBC News