NATO triggered its Response Force for the first time Friday to defend the eastern flank of the alliance, as Russian forces pushed deeper into Ukraine.
"In response to Russia's massive military buildup over the past months, we have all of us strengthened our deterrence and defense," NATO Secretary-General Jens Stoltenberg told reporters in Brussels. "We are deploying elements of the NATO Response Force on land, at sea and in the air, to further strengthen our posture and to respond quickly to any contingency."
"There must be no space for miscalculation or misunderstanding. We will do what it takes to protect and defend every ally and every inch of NATO territory," Stoltenberg said.
Several NATO allies have reinforced their presence in Eastern Europe in recent days, with troops, fighter jets and warships on high alert across the region.
NATO's priority is the defense of its members, said Claudia Major of the German Institute for International and Security Affairs. "European countries and NATO countries have to prepare for the repercussions of the war in the military domain, so assuring the defense of their own countries, [while] supporting Ukraine as much as they can," Major said. "They have to get prepared for the nonmilitary repercussions, like refugees, for example."
Ukraine's president again urged his country's Western allies to provide more military assistance. Wearing military fatigues, Volodymyr Zelenskyy gave a televised address Friday as Russian troops and armor advanced on Kyiv.
"This morning we are defending our state alone, as we did yesterday," he said. "The world's most powerful forces are watching from afar. Did yesterday's sanctions convince Russia? We hear in our sky and see on our earth that this is not enough. Foreign troops are still trying to become more active in our territory."
The Ukrainian president has vowed to remain in the capital despite acknowledging that he is a prime target for invading Russian forces.
Europe, the United States, Canada, Japan and Australia have announced wide-ranging sanctions against Russia aimed at blocking its banks from accessing funds and freezing the Kremlin out of Western financial markets.
Earlier this week, Russia's currency hit an all-time low against the dollar and its stock market plunged 40%. But that's unlikely to influence Russian President Vladimir Putin, said Nora Muller, executive director of international affairs at the Korber Foundation in Berlin.
"If we look at Putin's actions so far and the kind of decision-making that we can analyze, then he always put a higher priority to security considerations than he put to economic considerations," Muller told VOA.
Ukraine wants direct military support, which NATO has explicitly ruled out. Britain's Armed Forces Minister James Heappey explained his government's position to lawmakers Friday.
"British and NATO troops should not, must not, play an active role in Ukraine," Heappey said. "We must all be clear what the risk of miscalculation could be and how existential that could very quickly become if people miscalculate and things escalate unnecessarily."
Western intelligence assessments say Ukraine's armed forces have slowed the Russian advance, aided by weapons from Kyiv's allies, including the United States and Britain. But there is a limit to the military aid that the West can deliver, analyst Muller said.
"You cannot just deliver arms, especially when it's like complicated military systems and say, 'Here it is and you do with it whatever you like.' You do have to train people. And we may be beyond that stage already," Muller said.
Outside NATO headquarters, demonstrators called for tougher action. "We are fighting for the whole democratic world here. If we don't stop them in Ukraine, they will go next to the European Union," said Artemii Sattarov, a Ukrainian national living in Brussels.
Anger at Russia's actions — and frustration at the Western response — have triggered protests in cities around the world, from London to Pretoria, Amman to Buenos Aires, Taipei to Tel Aviv. In Russia itself, thousands of people have been arrested in recent days following anti-war protests in dozens of cities.
The Eiffel Tower in Paris and Berlin's Brandenburg Gate were among landmarks lit up in the yellow and blue colors of the Ukrainian flag. Kyiv has welcomed the gestures of support but says it needs weapons, not words.