Transatlantic bond 'strongest bulwark' against instability: Mattis

US Secretary of Defense James Mattis delivers an opening statement on the first day of the 53rd Munich Security Conference (MSC) at the Bayerischer Hof hotel in Munich, southern Germany, on February 17, 2017

The bond between Europe and America is the "strongest bulwark" against instability and violence, US Defence Secretary Jim Mattis said Friday as he tried to calm jittery allies seeking clarity from Donald Trump's White House.

International partners remain deeply troubled after Trump's campaign rhetoric questioned long-established alliances, and they worry about a growing scandal over possible ties between some of Trump's staff and Moscow.

"The transatlantic bond remains our strongest bulwark against instability and violence," Mattis told the Munich Security Conference.

"I am confident that we will strengthen our partnerships, confronting those who choose to attack innocent people or our democratic processes and freedoms."

Mattis, a retired four-star Marine general who spent years working with international partners, has often taken a divergent tone from his boss, hammering the importance of transatlantic ties and sounding a skeptical tone on the potential for military cooperation with Russia.

Trump has said he is open to closer cooperation with Moscow on Syria, particularly in the fight against the Islamic State jihadist group.

But Mattis told a NATO summit on Thursday that he is not "in a position right now to collaborate on a military level" with Moscow and said Russia must first "prove itself" and follow international law before envisioning any closer military ties.

Conference chairman Wolfgang Ischinger said the situation was unprecedented in modern history and described a "massive uncertainty" gripping the continent.

"European leaders and European governments are leaders are extremely impatient to find out what will really drive US foreign policy in this new period," he said, underscoring that many in Europe are clamouring to find out about the future of US-Russian relations.

The White House is still reeling from the forced resignation Monday of Trump's national security advisor, Michael Flynn, after he held pre-inauguration phone calls with the Russian ambassador about US sanctions policy.

Trump, who has repeatedly praised Russian President Vladimir Putin, on Thursday denied he or his staff had any pre-election contacts with Moscow.

"I have nothing to do with Russia," Trump said. "The whole Russia thing is a ruse."