As a meeting of alliance foreign ministers put on a united front on the need to counter Russian "aggression", Pompeo hammered home one of Trump's oldest themes -- demanding that NATO members pay their way.
Some allies, including Europe's economic powerhouse Germany, have been reluctant to meet a commitment made at a NATO summit in Wales in September 2014 to spend two percent of GDP on defence by 2024.
Trump has repeatedly declared this to be tantamount to countries not paying their dues, and former CIA boss Pompeo carried a tough message to NATO headquarters in Brussels.
Asked if Germany was doing enough to meet the target, Pompeo said bluntly: "No. They should meet the goals that they agreed to."
"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 the meeting.
Pompeo's comments came as German Chancellor Angela Merkel was heading to the White House for talks with Trump.
"NATO is wonderful, but it helps Europe more than it helps us," Trump said ahead of his meeting with the German leader.
- 'Fulfilling our obligations' -
His stark language contrasted with what Luxembourg's veteran Foreign Minister Jean Asselborn said was a more diplomatic approach in the meeting itself.
"Mike Pompeo of course insisted on the need for burden-sharing, but he did it without aggression," Asselborn told AFP.
"On the contrary he was attentive, he listened and took part in all the discussions."
As he arrived for the talks Germany's new Foreign Minister Heiko Maas stressed the contribution Berlin was making to humanitarian work in Syria and to Iraq.
He said Merkel's coalition government was in the middle of budget negotiations, but held out little prospect that they would lead to a defence spending boost.
And he stressed Germany "has an extraordinary presence in terms of its perception of its international responsibility and that we are also fulfilling our obligations to NATO."
Away from the harsh words on funding there was agreement among foreign ministers on the need to find ways to counter Russia's adoption of "hybrid warfare" techniques -- subversion, propaganda, cyber warfare -- to undermine the West without triggering a full NATO military response.
Pompeo sought to ease lingering concerns about Trump's commitment to NATO, saying the alliance was "more indispensible than ever" due to Russia's "unacceptable" actions, from Georgia to Ukraine to political meddling.
Noting that the talks were the first NATO ministerial meeting since Russian agents allegedly used a nerve agent to poison a former double agent in the English town of Salisbury, Britain's Foreign Secretary Boris Johnson summarised the dilemma.
"How do you deal with a military environment in which attacks come below the threshold of the Article 5 commitment to mutual support but do demand a common response?" he asked, referring to the alliance's mutual self-defence pact.
- 'Russian aggression' -
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