The United States is pressing European allies to ready more NATO battalions, ships and planes for combat, officials say, in a fresh move to shore up NATO’s deterrence against a potential Russian attack, Reuters reported.

U.S. Secretary of Defense Jim Mattis will seek broad agreement for the plan in Brussels on Thursday when alliance defense ministers meet, laying the ground for endorsement by NATO leaders at a summit in July, four U.S. and NATO officials and diplomats told Reuters.

The plan would require NATO to have 30 land battalions, 30 air fighter squadrons and 30 navy ships such as destroyers ready to deploy within 30 days of being put on alert, although the proposal does not discuss specific troop numbers or a deadline for setting up the strategy.

The size of battalions vary across NATO, from 600 to 1,000 soldiers.

This lays down a challenge for European governments, pilloried by U.S. President Donald Trump for slashing military spending after the Cold War, to remedy long-running problems with helicopters and jets that are grounded for lack of parts.

“We have an adversary (Russia) that can move quickly into the Baltics and Poland in a ground attack,” said one senior NATO diplomat who was briefed on the U.S. plans.