Britain, Germany and the United States moved forward with plans on Tuesday to lead a new NATO force on Russia’s border starting next year, but some eastern allies said the alliance’s effort must go further to deter Moscow.

Weeks before a critical NATO summit in Warsaw, three of NATO’s biggest military powers said they would each command a combat battalion across the eastern flank to help deter any sign of force such as that deployed by Moscow in Crimea in 2014.

“Britain will lead one of the battalions,” British Defense Secretary Michael Fallon said at a meeting of NATO defense ministers. “That should send a very strong signal of our determination to defend the Baltic states and Poland in the face of continued Russian aggression.”

The battalions are part of a broader NATO deterrent to be approved at the Warsaw summit on July 8, which will be involving troops on rotation, warehoused equipment and a highly mobile force backed by NATO’s 40,000-strong rapid reaction unit.

NATO hopes the plan can discourage Russia from staging the kind of campaign used to annex Ukraine’s Crimea peninsula in February 2014.

Berlin and Washington also said in Brussels that they would send troops to the new force, which is expected to amount to an estimated 4,000 soldiers, with contributions from other allies.

“There will be a continually present armored brigade combat team, which will bring in its own equipment with each rotation,” said U.S. Defense Secretary Ash Carter. He said that on top of that the United States would bring “a pre-positioned set of equipment for yet an additional armored brigade combat team which troops could fall in upon in a crisis.”

While eastern allies welcome the deployments in NATO’s biggest military build-up since the end of the Cold War, they want more support to defend against Russia’s powerful arsenal.

With a warning last week from a senior U.S. commander that the alliance would have only 72 hours notice of a missile or ground attack, Baltic nations and Poland want a sophisticated anti-missile shield to deter Russia from gaining the upper hand.

That could involve NATO fighter planes and surface-to-air missile interceptors on a much larger scale in the Baltics. Southern flank allies Bulgaria and Romania, meanwhile, are pushing for NATO to expand its maritime presence in the Black Sea, where Russia has a naval fleet, as well as more alliance troops to the region.

Russia sees NATO’s deterrence plans as hostile. Moscow’s envoy to the alliance has warned they threaten peace in central Europe. The Kremlin also says a U.S. ballistic missile shield, which Washington says is directed at protecting the alliance from Iran, is also escalating tensions.