The State Department says it is too early to determine who or what is responsible for a string of health issues that prompted some U.S. diplomats and their families to leave Cuba.
"This is a situation that we're still assessing," agency spokeswoman Heather Nauert told reporters on Thursday. "When I say an active investigation is underway, in part what that means is, we don't know exactly where this came from. We can't blame any one individual or a country at this point yet."
Some diplomats and staff members at the U.S. Embassy in Havana began to experience "a variety of physical symptoms" in fall 2016, according to Nauert, though she did not specify what symptoms.
The Associated Press, citing unnamed U.S. officials, reported Thursday that the symptoms included hearing loss attributed to a covert sonic device.
In turn, the State Department ordered two Cuban diplomats working in the country's embassy in Washington to leave the U.S. on May 23.
According to a statement released Wednesday by the Cuban government, the foreign ministry was made aware of the incidents on Feb. 17 and promptly launched an investigation into the matter.
The foreign ministry also denied any suggestion of wrongdoing and condemned the State Department's expulsion of its diplomats from the U.S., calling the decision "unjustified and unsubstantiated."
"The Ministry categorically emphasizes that Cuba has never, nor would it ever, allow that the Cuban territory be used for any action against accredited diplomatic agents or their families, without exception," the ministry said in a statement. "Moreover, it reiterates its willingness to cooperate in the clarification of this situation."