 -- After weeks of growing hostility between the U.S. and Cuba over "health attacks" on American personnel at the embassy in Havana, Cuba is firing back.

Cuban Foreign Minister Bruno Rodríguez Parrilla not only blamed the U.S. for politicizing the attacks, but also categorically denied that any attacks have occurred in a press conference in Washington Thursday.

The State Department has said that 24 Americans have been affected by mysterious targeted attacks that cause a range of symptoms including permanent hearing loss, loss of balance and dizziness, cognitive issues, and, in some cases, from mild traumatic brain injury. The U.S. has blamed Cuba for not taking care of its diplomats, but not for the attack themselves.

Rodríguez has now mounted Cuba's loudest defense yet.

"I can categorically affirm that those that say there have been attacks ... are deliberately lying," he said through a translator.

The foreign minister did not deny that American personnel may be experiencing symptoms and said his government is willing to continue the investigation to "find the truth." But so far, between the evidence that his government has collected and the significantly limited information it has received from the U.S., they do not believe the Trump administration.

"No attack has occurred. No deliberate action has taken place," he said. "If the U.S. government thinks otherwise, I invite it to present evidence."

The FBI and State Department's Diplomatic Security are investigating the incident. FBI teams have visited Cuba four times now, according to Rodríguez, who said they so far had "not presented any conclusion or any hypothesis as to what had happened or any specific incident."

Among the issues stumping investigators on both sides is what, exactly, is responsible for the symptoms and whether there is any sort of device capable of causing them. At first, American officials suspected there was a sonic device because personnel reported hearing screeching noises, but the U.S. has said there still is no known device or technology that has been identified as responsible.

The lack of a device has left Cuba suspicious, with Rodríguez saying today that no weapon or device could be the cause of all the reported symptoms. Cuba's preliminary investigation has concluded that "there is no evidence, no evidence whatsoever of the occurrence of the alleged incidents" or that the symptoms were even caused in Cuba.

"So far, I can confirm conclusively, those health problems cannot be the result of a single cause or single action," he said, and pointing to experts, claimed, "It is impossible to have a single cause explaining the diversity [of symptoms]."

Rodríguez urged the U.S. to share medical records and more specific details or convene Cuban and American doctors and investigators, so that his government can better understand the situation. One piece of evidence the U.S. has shared is the recording of the sound, Rodríguez said, but only altered versions -- which "did not comply with international standards," he said. Beyond that, "the cooperation received from the United States in this case has been very limited," he said.

Instead, he accused the Trump administration of using the health problems of staffers "as a pretext as a political context" to create "significant setbacks" in Cuban-American relations.

The U.S. has withdrawn the majority of its embassy staff in Havana, leaving only emergency personnel. Because of that, it has indefinitely suspended visa services at the U.S. embassy for Cubans trying to travel to America. In return for what they call Cuba's failure to protect Americans, the U.S. expelled 22 Cuban diplomats from Washington. And the State Department issued a travel warning for Cuba, telling the American public they too could be victims of the mysterious attacks.

Rodríguez accused the U.S. government of hypocrisy, questioning why U.S. authorities requested "212 visas for relatives and friends of diplomats between January and October" or "made more than 250 pleasure trips outside Havana" if the country is so unsafe. ABC News reached out to the State Department for confirmation -- and reaction to Rodríguez's other charges -- but has not yet heard back.

Symptoms were first reported late last year, affecting American diplomats, intelligence officials and some family members. In early 2017, the State Department said, it realized that there was a pattern and that personnel were being targeted. Cuba said it was told of the incidents in February and has been investigating ever since -- including by allowing the FBI to enter the once-Cold War enemy country.

State Department spokesperson Heather Nauert has said that the U.S. and Cuba are cooperating on the investigation, although they're not working together. But she has recently ramped up her tone about Cuba, too -- saying Cuba may have more information than it's sharing with the U.S.

"In a small country like Cuba that has the type of regime and government it does, they tend to know things that are going on within its own borders," she said in October.