Sen. Marco Rubio pushed back Sunday against comments from a Republican colleague that the United States has found no evidence of “sonic attacks” in Cuba.

The Florida Republican charged the attacks were a “documented fact.”

In a series of tweets Sunday, Rubio dismissed comments by Sen. Jeff Flake of Arizona, a longtime advocate for improving ties with Cuba, stating that any U.S. official briefed on the mysterious events in Havana “knows full well that while method of attack still in question, that attacks and injuries occurred isn’t.”

“It’s a documented FACT that 24 U.S. govt officials & spouses were victims of some sort of sophisticated attack while stationed in Havana,” Rubio tweeted.

Flake said Saturday that he has seen no evidence that American diplomats who suffered health symptoms while in Havana were “attacked,” according to the Associated Press.

After meeting with high ranking Cuban officials, Flake said classified briefings from U.S. officials had given him no reason to doubt Cuban officials who said there was no evidence any health symptoms were a result of an attack.

Rubio countered calling it impossible “to conduct 24 separate & sophisticated attacks" on U.S. government personnel without Cuban officials knowing.

The back and forth between the two senators sets up a potentially explosive hearing Tuesday at a highly anticipated Senate Foreign Relations subcommittee hearing chaired by Rubio. Members are expected to press State Department officials for more answers about the mysterious events.

The Trump administration has already pulled much of the U.S embassy staff from Havana and expelled 15 of their Cuban counterparts working in Washington.

The State Department has never accused Cuba of being behind the incidents. But it has repeatedly warned that Havana is responsible for the safety of foreign diplomats on its soil under the Vienna convention on diplomatic relations.