U.S. Secretary of Defense Jim Mattis will press European allies on Wednesday to stick to a promise to increase military budgets as the United States offers an increase in its own defence spending in Europe.
For the first time, NATO countries have submitted plans to show how they will reach a target to spend 2 percent of economic output on defence every year by 2024, after President Donald Trump threatened to withdraw support for low-spending allies.
Fifteen of the 28 countries, excluding the United States, now have a strategy to meet a NATO benchmark first agreed in 2014 in response to Russia's annexation of Ukraine's Crimea region, following years of cuts to European defence budgets.
It is unclear whether that will be enough to impress Trump when he attends a NATO summit in July.
"We cannot outsource Europe's security obligations to the United States," British Defence Secretary Gavin Williamson told reporters at the NATO defence ministers' meeting.
NATO data shows that Britain, Greece, Romania and the Baltic countries of Estonia, Latvia and Lithuania meet, or are close to, the 2 percent goal, while France and Turkey are among those countries set to reach it soon.
France plans to increase its defence spending by more than a third between 2017 and 2025, but Spain has said it will not meet the 2024 target. Belgium, the Netherlands, Luxembourg, Italy, Portugal, Norway and Denmark are also lagging, while Hungary expects to meet the goal only by 2026.
Germany, Europe's biggest economy, plans a multi-billion euro increase in defence spending but this is not enough to take it up to the 2 percent target by 2024.
Mattis is expected to take a tough stance with allies at the lunchtime meeting, said Katie Wheelbarger, U.S. deputy assistant secretary of defence for international security affairs.
"He will address those who don't have national plans to meet 2 percent and suggest they really need to develop those plans," she told reporters.
NOT JUST NUMBERS
The issue of low defence spending in Europe has long been an irritant in the United States, whose new national defence strategy centres on countering Russia after more than a decade of focusing on battling Islamist militants.
Military analysts say Europe is now vulnerable to a range of threats, including Russia's military modernisation, Islamist militancy and electronic warfare on computer networks.
One area of tension lies in the language of the NATO spending pledge of 2014. Allies committed to "move towards" 2 percent, but Trump now says 2 percent is the "bare minimum".
This week the Pentagon proposed its own increase of more than 30 percent in funding, primarily to deter Russia.
Some Europeans say focusing on the 2 percent figure is misleading as it does not take into account how money is spent.
Much of Belgian and British defence spending is set to be taken up by costly upgrades to fighter jet fleets, which military analysts say could come at the expense of other capabilities, such as sea patrols and infantry.
Germany is also one of the biggest troop contributors to NATO missions, from the Baltics to Afghanistan.
"It isn't just about dry figures," Germany's Defence Minister Ursula von der Leyen told reporters. "It's also about who is ultimately doing what."