Cuba: Canadian diplomat struck by headaches and hearing loss
Canada's foreign ministry is investigating after at least one of its diplomats stationed in Cuba was treated for hearing loss and headaches.
It comes a day after the US said its diplomats in Havana were experiencing strange physical symptoms.
Reports suggest the envoys could have been targeted by a covert sonic device that causes hearing loss.
Havana denies the allegation, but the US has removed two Cuban diplomats from Washington in retaliation.
"Cuba has never, nor would ever, allow the Cuban territory to be used for any kind of action against accredited diplomats or their families," Cuba's foreign ministry said.
While US officials have not directly accused the Cuban government, Secretary of State Rex Tillerson said the authorities in Havana needed to take action.
"We hold the Cuban authorities responsible for finding out who is carrying out these health attacks not just on our diplomats, as you've seen there are cases with other diplomats as well."
Global Affairs Canada, the country's foreign ministry, says the government is working with US and Cuban officials to find out what happened.
"We are aware of unusual symptoms affecting Canadian and US diplomatic personnel and their families in Havana," a spokesperson told the BBC.
"The government is actively working - including with US and Cuban authorities - to ascertain the cause. At this time, we do not have any reason to believe Canadian tourists and other visitors could be affected."
Analysis: Intrigue around a bizarre case
By Will Grant, BBC Cuba correspondent
As things stand, there are really more questions than clear answers. There has been a long history of mutual antagonism over the years between the US and Cuban diplomatic services. However, in the main it has been limited to either bold propaganda statements or to personal inconveniences.
In 2006 the Americans placed an electronic ticker tape on the outside of the then-US Interests Section in Havana and began broadcasting human rights messages. The Cubans then erected a "forest of flagpoles" to obscure the ticker from view. Surveillance is obviously commonplace and free movement around the country and banking services are restricted.
However, the idea of intentionally maiming US diplomats using a covert sonic device would be unprecedented. As such, some analysts consider it unlikely that this "device" was meant as a weapon, especially as the diplomats first noticed the symptoms towards the end of the Obama administration when relations between the Cuban Revolution and the White House were at an all-time high.
Cuba is conducting its own investigation and expressed a willingness to work with their US counterparts to determine the cause of the diplomats' unexplained symptoms. For now, in the absence of a plausible explanation, speculation is rife.
The Associated Press reported that a US investigation determined that the American diplomats' hearing loss could have been linked to sonic devices which emit inaudible sound waves that can cause deafness.
US officials, speaking to the agency anonymously, said investigations had determined devices had been deployed either inside or outside diplomats' homes.
Investigators are also considering the possibility that a third country, such as Russia, was behind the incidents, officials familiar with the inquiry told AP.
About five American diplomats, including some spouses, had been affected, but no children were involved, US officials said.
US Department of State spokeswoman Heather Nauer said staff began complaining of the strange symptoms late last year.
While they were not life-threatening, she revealed that a number of people had been brought home to the US as a result.
Washington and Havana only re-established ties in 2015, following 50 years of hostilities between the two countries.
Florida Senator Marco Rubio said the alleged incidents were just the latest examples of harassment toward US diplomats in Cuba.
"Personal harm to US officials shows the extent the Castro regime will go and clearly violates international norms," he said.
If true, the use of sonic devices to cause harm to diplomats would be unprecedented.