OTTAWA, April 16 (Xinhua) -- The families of Canadian diplomats serving in Cuba have been recalled as some Canadian diplomats and dependents are suffering unexplained brain symptoms, according to the Canada Press Monday.

Canadian officials said the ongoing problems are raising concerns about a new type of acquired brain injury, the cause of which remains unknown.

About 27 people from 10 diplomatic families underwent testing when some complained of dizziness, headaches and difficulty in concentrating.

As a favorite tourist destination for Canadians, Cuba annually attracts more than 1 million tourists, and Global Affairs Canada says there is no evidence of any related ailments among Canadian travellers.

The Canadian Foreign Affairs Ministry said Canada is currently working with the United States after the previous environmental assessment of its staff housing in March failed to turn up a cause. The U.S. personnel in Havana also took ill.

Over 20 U.S. diplomats and their family members in the Caribbean nation suffered symptoms such as hearing loss, tinnitus, vertigo, headaches and fatigue since the incidents were first reported in November 2016.

"According to the specialists, medical information raised concerns for a new type of acquired brain injury. Additional research is needed to better understand this," said a statement issued by the ministry Monday.

Canada and Cuba continue to have a positive and constructive relationship and have been cooperating to find a cause since problems first surfaced about a year ago, the statement said.

The symptoms developed amid concern about possible "acoustic attacks" in 2016 and 2017, which was regarded by Cuba as an unacceptable accusation without evidence.

Canadian officials said Monday that the theory of an acoustic or sonic attack has been ruled out.