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US Defence Secretary James Mattis hailed North Atlantic Treaty Organisation (NATO) as the "fundamental bedrock" of transatlantic security as he sought to reassure allies on Wednesday about President Donald Trump's commitment to the alliance.
"The alliance remains a fundamental bedrock for the United States and for all the transatlantic community, bonded as we are together," Mattis said as he met his counterparts in Brussels for the first time.
"It's a fair demand that all who benefit from the best defence in the world carry their proportionate share of the necessary cost to defend freedom," he added.
The 28-member organisation is trying to portray unity after Trump's previous comments that the alliance was "obsolete."
But Mattis's visit has been overshadowed by the resignation of Trump's national security adviser Michael Flynn over allegations he had discussed US sanctions with Russia's ambassador before taking office.
NATO chief Stoltenberg insisted the Flynn scandal was not a further cause for concern for the alliance, which has underpinned transatlantic security since the aftermath of World War II.
"I am absolutely certain that the message from this meeting will be a message of transatlantic unity," Stoltenberg said when asked about Flynn's resignation.
Stoltenberg said the ministers will also stress "the importance that we stand together and protect each other and a very strong commitment of the United States to NATO."
Mattis meanwhile praised the alliance for its enduring help for the United States in Afghanistan. "This has been the most successful alliance in military history," he said.
Also hanging over the meeting was a New York Times report that Moscow had deployed a new cruise missile, raising fears it would violate the Intermediate-Range Nuclear Forces Treaty (INF).
Like the US State Department, the NATO chief said he would not comment on intelligence matters but warned that "any non-compliance of Russia with the INF treaty would be of serious concern for the alliance.