BRUSSELS — A special fund set up for European requirements is not guaranteed to grow again next year after it received a nearly $2 billion increase in the fiscal 2019 budget request, U.S. Secretary of Defense Jim Mattis said Tuesday.

The Pentagon’s European Deterrence Initiative, initially called the European Reassurance Initiative, was created to help Eastern European allies rest easier and deter Russia from further incursion into Europe following what the West perceives as an illegal annexation of Crimea and continued aggression in the region.

The FY19 budget request included $6.5 billion for the EDI — an increase over the $4.8 billion requested in FY18 and a steep increase from the $3.4 billion received for FY17. But Mattis was clear that those year-over-year increases are no guarantee that another plus-up will be coming in FY20.

“No, I do not see it increasing every year going forward,” Mattis told reporters while traveling in Europe.

However, asked if that meant this year’s EDI figure would be the high watermark for the account, Mattis said everything would be decided based on the situation in Europe at the time. He reiterated a call for NATO nations to develop plans to spend 2 percent of gross domestic product on defense, a target encouraged by the alliance.

“We are where we’re at. We’re in good position. We also see the rest of the alliance climbing in their commitment,” Mattis said.

His comments came hours after NATO Secretary General Jens Stolenberg announced that eight NATO nations would hit the 2 percent GDP target this year, and that by 2024, 15 of the 29 nations should be there.

“This is substantial progress and a good start. But we still have a long way to go,” Stoltenberg said Tuesday.

Jen Judson in Washington contributed to this report.