President Trump will press NATO allies to fulfill key defense spending commitments at a summit in Turkey this week.
The pressure follows pledges secured from member nations last year.
NATO's chief has requested that allies submit robust plans to reach spending goals.
U.S. officials have characterized heightening tensions as "growing pains."
Reports indicate allies will receive "report cards" to track their progress.
Various experts have cautioned of financial consequences if the demands are enforced fully.