At least one Canadian diplomat in Cuba was treated for hearing loss; the Canadian government has said, a day after media reports said a group of American diplomats in Havana suffered similar symptoms.
Brianne Maxwell, a spokeswoman for Canada's foreign ministry, said on Thursday officials "are aware of unusual symptoms affecting Canadian and US diplomatic personnel and their families in Havana.
"The government is actively working - including with US and Cuban authorities - to ascertain the cause."
Maxwell said officials don't have any reason to believe visitors could be affected.
US officials attributed the severe hearing loss to an advanced sonic device, according to the Associated Press news agency.
The Cuban government said it "has never permitted, nor will permit, that Cuban territory be used for any action against accredited diplomatic officials or their families, with no exception".
In a statement late on Wednesday, the Cuban foreign ministry said it launched an "urgent investigation" after being informed of the incidents in February.
Heather Nauert, a spokeswoman for the US State Department, said the two Cuban diplomats were asked to leave in May after diplomats began suffering "a variety of physical symptoms".
Cuba called the expulsions "unjustified and baseless".
The AP reported that the US move came after an investigation concluded that the diplomats had been attacked with an advanced sonic weapon.
Nauert did not say how many US diplomats were affected nor confirmed they had suffered hearing loss.
US officials, who spoke on the condition of anonymity, told the AP that some of the diplomats' symptoms were so severe that they were forced to cancel their tours early and return home.
About five diplomats, several with spouses, were affected, the AP said.
The device operated outside the range of audible sound and had been deployed either inside or outside their residences, the officials said.
It was not immediately clear if the device was a weapon used in a deliberate attack, the AP said.
Investigators are looking into the possibility that the incidents were carried out by a third country, officials familiar with the probe told AP.
If true, the use of sonic devices to harm diplomats would be unprecedented.
The US embassy in Havana reopened in 2015 as part of President Barack Obama's re-establishment of diplomatic relations with Cuba.
Source: AP news agency