Cuban dictator Raul Castro's regime is hiding information that might explain mysterious attacks on American officials in Havana, according to Sen. Marco Rubio.

"No one should be fooled by the Castro regime's claim it knows nothing about how these harmful attacks are occurring or who perpetrated them," Rubio said Tuesday.

With that in mind, Secretary of State Rex Tillerson's expulsion of 15 Cuban diplomats won praise from the Florida Republican, who'd sharply criticized the State Department's earlier response to the incidents. But the State Department maintained the decision did not amount to an assessment that Castro's regime is behind the attacks, so the punishment drew mixed reviews from other lawmakers and proponents of engagement with Cuba.

"We need to be smart and thoughtful in responding to these attacks," said New York Rep. Eliot Engel, the top Democrat on the Foreign Affairs committee. "Unfortunately, today's response was extremely shortsighted."

Engel, who "strongly supported" Tillerson's decision last week to withdraw most U.S. officials fro Havana, suggested the United States is being duped by a third-party attacker.

"It appears that this plays right into the hands of a potential rogue actor, Russia perhaps, that is trying to create a further wedge between our two countries and other nations in the hemisphere," Engel said.

Cuba and Russia have had friendly relations dating back to the height of the Cold War, with the Cuban missile crisis the most dramatic demonstration of those ties. More recently, Cuban diplomats have held a series of meetings with Russian counterparts, including a July trip to Moscow by the Cuban diplomat responsible for U.S.-related issues; those meetings took place in the run-up to announcements from Russia and Cuba in opposition to U.S. sanctions on Venezuela.

Such moves, taken together with mysterious attacks on 22 American diplomats, have renewed some congressional opposition to former President Barack Obama's effort to normalize relations with Cuba.

"All nations have an obligation to ensure the protection of diplomatic representatives in their countries," Rubio said. "Cuba is failing miserably and proving how misguided and dangerous the Obama administration's decisions were."

The State Department issued a travel warning that U.S. citizens in Cuba could be "at risk" of suffering the kinds of ailments apparently inflicted upon American diplomats. But Tillerson's team has stopped short of cutting all diplomatic engagement with the regime.

"Investigations into the attacks are ongoing, as investigators have been unable to determine who or what is causing these attacks," a State Department official told reporters Tuesday morning. "The Cuban government has told us it will continue its investigation into these attacks, and we will continue to cooperate that — with them in this effort. We will also continue our own investigations into these attacks."