HAVANA - The Cuban Foreign Ministry said on Wednesday it had started an "exhaustive" investigation into the bizarre incidents which the United States said had caused physical symptoms in its diplomats serving here. The matter had also resulted in the expulsion of two Cuban diplomats from Washington in late May.

Earlier on Wednesday, US State Department spokeswoman Heather Nauert told reporters that the exact nature of the incidents was unclear, but that the affected US citizens had returned to the US for non-life-threatening "medical reasons." She didn't give the number of the US citizens affected.

"We don't have any definitive answers about the source or the cause of what we consider to be incidents," she said, adding that "we take this situation very seriously".

Reports said the affected US citizens, who first reported in fall of 2016 that some incidents were causing physical symptoms, suffered a severe hearing loss.

The Cuban Foreign Ministry statement released late on Wednesday said Havana complies strictly and seriously with its obligations under the Vienna Convention on Diplomatic Relations of 1961 regarding the protection and security of diplomatic agents.

"Cuba has never, nor would it ever, allow that the Cuban territory be used for any action against accredited diplomatic agents or their families," said the statement. "Cuba reiterates its willingness to cooperate in the clarification of this situation."

Cuba said it had started a comprehensive investigation into the alleged incidents after it had been informed of them by the embassy in February.

"Various entities conducted an exhaustive, high-priority, urgent investigation ordered by the highest authorities of the Cuban government and requested the US embassy to share information on these incidents," said the statement. Meanwhile, Cuba had strengthened security around the US embassy, diplomatic and staff residences.

The Cuban Foreign Ministry statement also called the US decision to expel two Cuban diplomats based in Washington "unjustified and baseless."

The US and Cuba officially resumed diplomatic relations in July 2015, more than five decades after they were severed.

Xinhua