Nato leaders are meeting near London, as tensions between members threaten to overshadow a summit marking the military alliance’s 70th birthday.
The three-hour talks are expected to cover issues such as cyber-attacks and the strategic challenge posed by China.
In opening remarks, UK Prime Minister, Boris Johnson, reminded members of the alliance’s principle of “one for all, and all for one”.
Tuesday saw sharp exchanges between the US and French leaders over many topics.
The highly choreographed anniversary gathering, intended to show unity, has been unable to hide deep differences between Nato members, BBC Defence Correspondent Jonathan Beale reports.
Although the 29-member bloc’s future is not in doubt, there are disagreements over Turkey’s recent military action in northern Syria, the levels of military spending by members and recent controversial comments by French President Emmanuel Macron that the alliance is “brain dead”.
At the start of the meeting at a luxury resort near Watford, Mr Johnson said: “As long as we stand together no-one can hope to defeat us.” The gathering follows receptions held on Tuesday at Buckingham Palace and Downing Street.
Nato started out in 1949 with just 12 countries as members but having now expanded to a bloc of 29 it is increasingly difficult for the alliance to project a united front.
Two key issues have loomed over this summit: defence spending – a longstanding issue of concern for the US, which militarily dominates the group – and relations between Turkey and other member states.
Before departing for London, Mr Erdogan said he would oppose a Nato defence plan for the Baltic region if the bloc did not support Turkey over its fight against Kurdish groups in Syria it considers terrorists.
But other leaders, including Mr Macron, have made clear they oppose such a move, not least because Kurdish-led forces drove IS militants out of a quarter of Syria with the help of a US-led multinational coalition.
