The leaders of NATO's 29 member states will hold a special summit in London in December to mark the alliance's 70th anniversary, Secretary-General Jens Stoltenberg said on February 6.

"The meeting in London will be an opportunity for allied heads of state and government to address the security challenges we face now and in the future, and to ensure that NATO continues to adapt in order to keep its population of almost 1 billion people safe," Stoltenberg said in a statement.

Stoltenberg said the British capital was the ideal setting to mark 70 years of transatlantic military cooperation.

"London was the home of NATO’s first headquarters. The United Kingdom was one of the alliance’s 12 founding members and continues to play a key role in the alliance, making essential contributions to our shared security," the statement said.

NATO's founding act, the North Atlantic Treaty, was signed on April 4, 1949, in Washington by the United States, Canada, Britain, France, Italy, Netherlands, Norway, Denmark, Portugal, Belgium, Iceland, and Luxembourg.

Greece and Turkey joined together in 1952, followed by West Germany in 1955 and Spain in 1982.

After the fall of communism, Poland, the Czech Republic, and Hungary became members in 1999, followed by a second wave of expansion in the former Eastern Bloc in 2004, which brought Romania, Bulgaria, Estonia, Latvia, Lithuania, Slovakia, and Slovenia into the alliance.

Albania and Croatia were next, joining in 2009, and Montenegro became the newest NATO member in 2017.

Stoltenberg's announcement came as NATO signed an accession agreement with Macedonia on February 6, after a historic deal that removed Greece's objections and normalized relations between the neighbors.