At least 16 US embassy staff have been affected by hearing loss, in what has previously been dubbed an acoustic attack, while working in Cuba, US officials have revealed.

US State Department spokeswoman Heather Nauert said that two weeks ago the State Department learned of incidents at its embassy in Havana in late 2016.

She said they "caused a variety of physical symptoms" in US government employees, but added that the attacks now appear to have ceased.

"We can confirm that at least 16 US government employees, members of our embassy community, have experienced some kind of symptoms," she said.

Several US citizens at the embassy were evacuated over the past six months for treatment of a variety of complaints. Some subsequently received hearing aids.

Cuba has denied any involvement.

A doctor who evaluated US and Canadian diplomats working in Cuba diagnosed them with conditions as serious as mild traumatic brain injury and damage to the central nervous system, CBS News said this week, citing medical records it reviewed.

The diplomats had complained of symptoms including hearing loss, nausea, headaches and balance disorders after what were described as "incidents" that began affecting them in Havana beginning in late 2016, CBS News said.

Officials are investigating whether the diplomats were targets of some form of sonic attack directed at their homes, CBS reported, citing a source familiar with the incidents.

The source said the incidents had continued to occur on the Communist-ruled island and that some US diplomats had cut short their assignments there.

Although Washington expelled two Cuban diplomats over the incidents, Cuba has said it was investigating the US allegations and would never allow its territory to be used for any action against diplomatic personnel or their families.

"The Cuban government has assured us it is also investigating and taking appropriate measures," the State Department spokeswoman said.

Asked about the CBS report, the US State Department said it did not have "definitive answers" on the source or cause of the incidents.

A spokeswoman for Canada's foreign ministry said Canada likewise was working to determine the cause.

"At this time, we do not have any reason to believe Canadian tourists and other visitors could be affected," a spokeswoman said.