Stoltenberg tweeted that the British capital was "the ideal setting to mark 70 years of transatlantic military cooperation, as the home of NATO's first HQ back in 1949".

NATO chiefs will be hoping to avoid the high drama of last year's summit in Brussels, when US President Donald Trump launched a blistering attack on allies, in particular Germany, for not spending enough on defence.

There had been talk of holding the leaders' meeting in Washington -- where NATO's founding treaty was signed -- but, amid fears of a new transatlantic bust-up, foreign ministers will gather in the US capital in April instead.

Estonia also offered to host the December meeting.

"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 one billion people safe," Stoltenberg said in a statement.

Though it will gather the alliance's top leaders for talks, the meeting will not have the formal status of a summit.

NATO summits are usually held every two years and conclude with a formal, binding statement of aims and actions agreed by all allies -- such as the 2014 agreement to try to spend two percent of GDP on defence.

It is yet to be confirmed whether a statement will be issued at December's meeting, but one was not given at the last such gathering in Brussels in 2017.

The anniversary comes at a delicate time for NATO, with concerns lingering about Trump's commitment to the alliance and his willingness to honour its mutual self-defence pact.

From the US side, Trump has been unstinting in his criticism of NATO's European members, accusing them of freeloading on the protection offered by the US military while not spending enough on their own armed forces.

Before taking office Trump called NATO "obsolete" and soon after July's tumultuous summit, he questioned whether the US would honour the alliance's founding principle of mutual defence for newest member Montenegro.