U.S. Strategic Command head Gen. John Hyten said the U.S. had "no defense" for Russia's SSC-8 nuclear-capable cruise missiles in Europe.
Despite holding opposing views on NATO and the Syrian war, Russia and Turkey held joint naval exercises in the Black Sea, where military drills have already heightened tensions.
Recent Russian deployments suggest a new intervention in Ukraine, Belarus or the Caucasus.
Russia's Yasen-class Kazan nuclear submarine was designed to hold long-range Kalibr cruise missiles, supersonic Oniks cruise missiles and more deadly weapons.
Lithuania, Latvia and Estonia, part of both NATO and the European Union, have been increasingly nervous since the Russian takeover of Crimea in 2014.
Putin fears that democracy in Ukraine will spread to Russia. And end his reign.
The used Adelaide frigates could cost Poland as much as $700 million.
Russia fired missiles only miles away from NATO forces in the volatile Black Sea region, where the U.S. has accused Moscow of threatening its interests.
Serbia's Defense Minister Zoran Djordjevic said Russia would provide his country with free jets, tanks and armored vehicles as Moscow seeks to increase its Balkans influence.
If the invasion of Crimea aimed to thwart NATO, it has backfired spectacularly.
NATO has planned to spend over $3.2 billion on a large boost to the 28-member military alliance's electronic and satellite communication defense systems.
Demonstrators in Bern held up a sign reading "Kill Erdogan with his own weapons."
Russia has up to 5,000 military personnel operating inside the rebel Donbas.
Tillerson's potential no-show had increased unease caused by U.S. President Donald Trump's description of NATO as "obsolete" during his election campaign.
The world will only notice the absence of U.S. leadership when it is gone and catastrophe strikes.
Tillerson argued that Montenegro's membership in the alliance would support greater integration, democratic reform, trade, security and stability among its neighbors.
The decisions to skip the NATO meeting and to visit Moscow risked feeding a perception that Trump may be putting U.S. dealings with big powers before those of smaller nations.
A day after meeting Angela Merkel, Trump tweets the 'United States must be paid more for the powerful, and very expensive, defense it provides to Germany.'
The German leader is said to be meticulously preparing for her first in-person meeting with the U.S. president.