U.S. NAVAL BASE GUANTANAMO BAY, Cuba — The U.S. military quietly conducted a joint exercise last week with the Cuban army on either side of the perimeter of the U.S. naval base at Guantanamo Bay in southeastern Cuba.

About 150 U.S. and Cuban uniformed and civilian personnel took part in the drill, which saw Cuban military helicopters cross to the American side of the fence, and American and Cuban medics establish a triage centre on Cuban territory.

U.S. military officials said nothing about the exercise ahead of — or during — the event last Thursday, despite the presence elsewhere on the 116-square-kilometre base of 28 journalists from global media outlets to cover the scheduled appearances of terror suspects in the military tribunals.

News the exercise took place is likely to enrage Cuban exiles and their supporters, some of whom include prominent Republican members of Congress.

The U.S. has no diplomatic relations with Cuba. But U.S. President Barack Obama has called past U.S. policy on Cuba a failure and recently eased restrictions on visits to the island by Cuban-Americans.

One military spokesperson said they weren't planning on talking about the drill. Later, another provided information from a prepared account, saying the exercises had been underway annually for a decade at the base.

The account said Thursday's drill had taken place in the vicinity of the Northeast Gate — the only crossing point between the base and Cuba.

It also said co-ordination for the event had taken place at the "fenceline" meetings the military has long admitted exist between the two countries so that officials can avert potential misunderstandings along the perimeter.

"The bilateral fenceline drill exercises began in 1999, when the U.S. naval station and Cuban authorities agreed to conduct annual first responders and emergency response drills at the Northeast Gate," said navy Lt.-Cmdr. Brook DeWalt, speaking from the prepared account.

"The exercise allows the two countries to co-ordinate and practise emergency support operations in the event of a natural disaster such as brush fires."

DeWalt added the exercise simulated a large brush fire — actually burning wood and tires — occurring along the fenceline.

"Helicopters of the Cuban Frontier Brigade crossed the lines to conduct a water drop to extinguish the fire," he said.

"There was . . . a mass casualty drill conducted where U.S. naval hospital and Cuban frontier medical brigade personnel established