Under a scorching sun, about a dozen US Marines armed with assault rifles simulated storming a bunker at the former US Fort Sherman base near the Atlantic entrance to the Panama Canal.

The facilities now serve as a training ground for US Marines and Panamanian police under a cooperation program launched in August.

Panama said about 50 US Marines would train from October 9 to 29 in its jungle to improve their skills "in one of the most demanding environments."

"This training is purely aimed at our defense and protection" to fight "organized crime and drug trafficking," Panamanian Major Didier Santamaria told AFP.

A similar course in August "focused only on survival; this one adds some tactics and jungle tracking," said US Colonel Ada Cotto.

The mission is to "create knowledge and mutual relationships" that can be shared "for both countries," she said.

The drills come amid tension between the United States and Venezuela, whose president Nicolas Maduro accuses Washington of plotting to overthrow him.

Washington has sent several warships and thousands of troops to Caribbean region.

But Cotto denied any link between the US exercises and plans to intervene in Venezuela.

"We are not preparing for anything," she said when asked if the training was related to the Venezuelan crisis.

"Everything is transparent and by invitation of the Panamanian government," she added.

The agreement was signed amid pressure from US President Donald Trump, who threatened to take control of the Panama Canal, refusing to rule out the use of force.