NATO-member defense spending may come back into focus as former U.S. President Donald Trump returns to office.

"Time is ticking," said Ed Arnold, a senior research fellow for European security at the Royal United Services Institute.

NATO chief Mark Rutte congratulated Donald Trump on Wednesday for being elected president of the United States, and emphasised that members were increasing their military spending, a response to a persistent Trump criticism of the Western alliance.

NATO chief vows to maintain a ‘strong’ alliance NATO Secretary General Mark Rutte has also congratulated Donald Trump on his victory, saying his leadership will be key to keeping the alliance strong.

US allies at NATO scrambled Wednesday to put a brave face on the return of Donald Trump to the White House amid fears the unpredictable Republican could upend European security and pull the plug on Ukraine support.