The United States and Britain kept up the pressure on their European allies to increase national defence spending at a meeting of NATO foreign ministers on Friday.
"As [US] President [Donald] Trump has made clear, it is no longer sustainable for the US to maintain a disproportionate share of NATO's defence expenditures," the new US Secretary of State Rex Tillerson told his NATO counterparts in a speech.
Tillerson, who made his maiden appearance at the gathering, was supported in his demands by British Defence Minister Michael Fallon.
Only five members currently meet the target and "others must now raise their game," Fallon told reporters at a press conference in London.
Earlier German Foreign Minister Sigmar Gabriel described NATO's target of each country increasing defence spending to 2 per cent of gross domestic product (GDP) as "unrealistic."
Gabriel said that hitting the defence target would mean allocating 70 billion euros (74.8 billion dollars) per year for military purposes in Germany, hence doubling the current budget.
"I don't know a single politician in Germany who thinks that this is achievable in our country, let alone desirable," Gabriel said.
The relationship between the new US administration and NATO got off to a rocky start after Trump called the alliance "obsolete" and criticized NATO allies, including Germany, for failing to meet NATO spending targets.
Tillerson kept up the pressure in his speech.
"Allies that do not have a concrete plan to spend 2 per cent of GDP on defence by 2024 need to establish one now. Allies that have a plan to reach the 2-per-cent guideline need to accelerate efforts and show results," he said.
NATO Secretary General Jens Stoltenberg said that spending more on defence was in the interest of everyone, given the security threats on Europe's borders.
"Increased defence spending is not about pleasing the United States," Stoltenberg said.
"It's about investing more in European security, because it is important for Europe. Europe is close to the turmoil and violence we see in North Africa, in the Middle East, Iraq and Syria. And Europe is close to a more assertive Russia willing to use force against their neighbour in Ukraine."
The decision by NATO to hold the meeting earlier than originally planned was widely seen as an effort to accommodate Tillerson, who had said that he would not be able to attend during the originally scheduled session on April 5-6.
Tillerson's original plan to miss the NATO meeting but travel to Russia later in the month raised eyebrows about the White House's priorities.
NATO ministers also agreed at the meeting to step up efforts in Iraq, by training Iraqi paramedics in military medicine, as well as providing additional support for the maintenance of tanks and armoured fighting vehicles.
Friday's meeting paves the way for a meeting of NATO leaders in Brussels on May 25, which Trump is expected to attend.