Ahead of President Trump's meeting with NATO Secretary General Jens Stoltenberg in Washington, senior White House officials said the US supports Montenegro's investigation into the alleged Russian-backed plot to thwart the Balkan nation from joining the western security alliance.
'If other countries pay their fair share rather than relying on the United States to make up the difference, we will all be much more secure, ' Mr Trump told reporters.
'I complained about that a longer time ago and they made a change and now they do fight terrorism. "I think that the secretary general has made clear that he also views it as a priority to get allies to shoulder a greater burden of defense investment and so the president and secretary general are likely to see eye to eye on that issue", the official said.
Germany, for instance, has committed to ratcheting up its spending to 2 percent of GDP by 2024, a decision Trump praised Merkel for during a joint press conference at the White House last month.
"I said it was obsolete", Mr Trump said.
In an interview with the New York Post, Trump was asked about infighting among top members of his administration in which Bannon is said to be a center figure.
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He went on to say that relations between the two countries "may be at all time low".
Trump's comments came amid heightened tensions over Moscow's backing of Syrian President Bashar al-Assad following a suspected chemical weapons attack in Syria last week. "No. 2, the countries aren't paying what they're supposed to pay", Trump said in January.
Trump's evolution was likely impacted by his decision last week to launch 59 Tomahawk cruise missiles against the Syrian government, a move that prompted backlash from Moscow, according to a USA officials who briefed reporters Wednesday on condition of anonymity.
Trump's comments come less than a week after he ordered missile strikes on a Syrian airfield after US evidence indicated that Assad killed civilians using the nerve agent sarin. "I think it's wonderful that they abstained", he said.
More than half of Montenegro's 620,000 inhabitants are opposed to North Atlantic Treaty Organisation membership, according to recent polls. But he added: "We have to find ways to live with them, to avoid a new cold war".
Under Russian leader Vladimir Putin, the Kremlin has long seen the Balkans as inside its "sphere of influence". "I think he had a very successful meeting with Russian Federation".