Defence ministers and leaders from dozens of NATO countries attended a security conference in the German city of Munich.
Russian Foreign Minister Sergey Lavrov and US Vice President Joe Biden were among those who gathered there.
During his speech, Biden tried to dispel fears that the US had moved its focus away from Europe.
The conflict in Syria is also one of several issues on the agenda - and UN Special Envoy Lakdhar Brahimi has also been speaking.
Al Jazeera's Jonah Hull reports from Munich.