Echoing a regular theme of his boss President Donald Trump, Pompeo said European countries needed to do more to increase their military spending and thus reduce the burden placed on the alliance's biggest member.

Some allies, most notably wealthy Germany, are reluctant to meet a commitment made at a NATO summit in Wales in September 2016 to spend two percent of their GDP on their military by 2024.

Asked if Germany was doing enough to meet the commitment, former CIA director Pompeo said bluntly: "No. They should meet the goals that they agreed to."

Pompeo's comments came as German Chancellor Angela Merkel was heading to the White House for talks with Trump.

"European nations must bear the necessary responsibilities for their security and make the case to their fellow citizens why it is critical to fulfil their obligations on defence spending," Pompeo told reporters after a meeting of NATO foreign ministers in Brussels.

Trump has repeatedly declared this to be tantamount to countries not paying their dues, with US officials regularly singling out Germany -- Europe's richest country -- for criticism.

A senior US official said Germany spends only 1.24 percent of its GDP on defence and plans only to increase this to 1.25 percent by 2021.