Canada has no plans to remove diplomats from Cuba after at least eight people connected to its embassy appeared to have contracted symptoms of a potential illness at the centre of a rift in US-Cuba relations, a senior government official said.

The official said the eight were among 27 people screened following US reports that two dozen American officials and family members in Havana had been suffering a range of unexplained symptoms including nausea, dizziness, headaches and nosebleeds.

The eight were said to have required follow-up treatment but were not hospitalised, and there was no reason to close the embassy in Havana.

Canadian investigators have not come up with an explanation for the illnesses.

There are 20 Canadian families with connections to the embassy and people from half of them came forward to be tested after the US reported that some of its personnel and family members had experienced a range of ailments, some after hearing an unusual sound. For most, the symptoms occurred around May 2017.

The Royal Canadian Mounted Police is leading an investigation into the situation but has not yet found any evidence that anything was done intentionally to the people who reported symptoms, the official said.

Washington says 24 US government officials and spouses fell ill in Havana in their homes and some hotels starting in 2016.

US Secretary of State Rex Tillerson said the symptoms were the result of an attack, but the FBI has found no evidence of one. Neither has Canada.

A different senior Canadian official said the government had not found any evidence that anyone was attacked.

Tillerson has said he is "convinced these were targeted attacks", but the US does not know who is behind them.

The US has withdrawn most of its diplomats from Havana, citing a health risk, and forced many Cuban diplomats to leave Washington.

Cuba has repeatedly and adamantly denied involvement or knowledge of any attacks and has decried the reductions as an unjustified blow to US-Cuban relations that were restored under President Barack Obama.

The lack of answers more than a year after the incidents started has emboldened Cuba's defenders to argue the US cannot be certain anyone was harmed intentionally since no proof has been publicly presented.

But top State Department officials testifying before the Senate Foreign Relations Committee this week said they were sure it was an attack of some kind.