NATO leaders will display their resolve towards a resurgent Russia at a summit in Warsaw on Friday despite what many see as a weakening of the West due to Britain's vote to leave the European Union.
U.S. President Barack Obama, attending his last summit of the Western defense alliance before he leaves office next January, will urge European allies to stand firm over Russia's annexation of Crimea and its support for Russian-speaking rebels in eastern Ukraine.
The 28-nation alliance will formally agree to deploy four battalions with 3,000 to 4,000 troops in the Baltic states and eastern Poland on a rotating basis to reassure eastern NATO members of its readiness to defend them.
"This is a defining moment for our security," NATO Secretary-General Jens Stoltenberg told a new conference with Polish President Andrzej Duda on Thursday. "NATO is responding with speed and determination."
Estonia, Latvia, Lithuania and Poland requested a permanent NATO presence amid fears that Moscow could seek to destabilize their pro-Western governments through cyber attacks, stirring up Russian speakers, hostile broadcasting and even territorial incursions. Critics say the NATO plan is a minimal trip wire that might not deter Russian action.
The Kremlin denies any such intention and says NATO is the aggressor by moving its borders ever closer onto former Soviet territory which it regards as its sphere of influence.
President Vladimir Putin has made several gestures that seem aimed at defusing tension ahead of the summit, even as Moscow highlights its intention to deploy nuclear-capable missiles in Kaliningrad, a Russian enclave between NATO nations.