The Pentagon has refused to rule out military intervention on Venezuela’s border, a day after John Bolton, the US national security adviser, was photographed carrying a notepad that read: “5,000 troops to Colombia”.

Patrick Shanahan, the acting defence secretary, was asked repeatedly whether Mr Bolton’s notes indicated a deployment.

"I’m not commenting on it,” he said. “I haven't discussed that with Secretary Bolton."

Mr Bolton on Monday would not rule out the use of US troops in Venezuela.

"The president has made it clear on this matter that all options are on the table," he said.