Republican Senator John McCain has broken with the reassuring message US officials have sought to convey on their debut trip to Europe, saying the Trump administration is in “disarray”.

Senator McCain, a known Trump critic, told the Munich Security Conference in Germany on Friday the resignation of the Donald Trump’s security adviser, Mr Michael Flynn, over his contacts with Russia reflected deep problems in Washington.

“I think that the Flynn issue obviously is something that shows that in many respects this administration is in disarray and they’ve got a lot of work to do,” said Senator McCain, even as he praised Trump’s defence secretary, Mr James Mattis.

“The president, I think, makes statements (and) on other occasions contradicts himself. So we’ve learned to watch what the president does as opposed to what he says,” he said.

European governments have been unsettled by the signals sent by Trump on a range of foreign policy issues ranging from NATO and Russia to Iran, Israel and European integration.

The debut trip to Europe of Mr Mattis and Secretary of State Rex Tillerson, to a meeting of G20 counterparts in Bonn, went some way to assuaging concerns as they both took a more traditional US position.

But Mr Trump is wrestling with a growing controversy at home about potential ties between his aides and Russia, which he dismissed on Thursday as a “ruse” and “scam” perpetrated by a hostile news media.

Mr Mattis made clear to allies – both at NATO in Brussels and in Munich – the US would not retreat from leadership as the European continent grapples with an assertive Russia, wars in eastern and southern Mediterranean countries and attacks by Islamist militants.

US Vice-President Mike Pence will address the Munich conference on Saturday with a similar message of reassurance.

Mr Pence will say that Europe is an “indispensable partner” for the US, a senior White House foreign policy adviser told reporters.

Mr Mattis told a crowd that included heads of state and more than 70 defence ministers that Mr Trump backed NATO.

“President Trump came into office and has thrown now his full support to NATO. He too espouses NATO’s need to adapt to today’s strategic situation for it to remain credible, capable and relevant,” Mr Mattis said.