Artillery fire escalated sharply in eastern Ukraine on Saturday and thousands of residents fled the region in chaotic evacuations — two developments rife with opportunities for what the United States has warned could be a pretext for a Russian invasion.
Russian-backed separatists, who have been fighting the Ukrainian government for years, have asserted, without evidence, that Ukraine was planning a large-scale attack on territory they control.
Western leaders have derided the notion that Ukraine would launch an attack while surrounded by Russian forces, and Ukrainian officials dismissed the claim as “a cynical Russian lie.”
But separatist leaders on Saturday urged women and children to evacuate, and able-bodied men to prepare to fight. And the ginned-up panic was already having real effects, with refugees frantically boarding buses to Russia and refugee tent camps popping up across the Russian border.
At the same time, the firing of mortars, artillery and rocket-propelled grenades by separatist rebels along the front line roughly doubled the level of the previous two days, the Ukrainian Ministry of Internal Affairs said. Two Ukrainian soldiers were killed and five wounded, the military said.
Ukrainian officials said the shelling came exclusively from the separatists, who are seen as a proxy for Russia.
New York Times reporters at the scene witnessed shelling from separatists and saw no return fire from the Ukrainian forces, although residents in the separatist regions said there was shelling from both sides.
“I have a small baby,” said Nadya Lapygina, who said her town in the breakaway region of Luhansk was hit by artillery and mortar fire. “You have no idea how scary it is to hide him from the shelling.”
In a pointed reminder of where this conflict could lead, Russia engaged in a dramatic display of military theater on Saturday, test-firing ballistic and cruise missiles. President Vladimir V. Putin of Russia presided over tests of nuclear-capable missiles as part of what Russia insists are nothing more than exercises and not the precursor to an invasion.
Tensions between the United States and Russia have not been this high since the Cold War, and Russia’s nuclear drills appeared carefully timed to deter the West from direct military involvement in Ukraine.
Western leaders gathering in Munich issued repeated calls for a diplomatic resolution to the crisis, despite President Biden’s claim on Friday that Mr. Putin had already decided to invade Ukraine.
The leaders displayed a remarkably united front in what Vice President Kamala Harris called “a defining moment” for European security and the defense of democratic values.
But in Ukraine, the fighting edged perilously closer to a tipping point. And there were alarming signs of what American officials described as possible precursors to a pretext for a Russian invasion.
Intense artillery barrages targeted a pocket of government-controlled territory around the town of Svitlodarsk, a spot that has worried security analysts for weeks for its proximity to dangerous industrial infrastructure, including storage tanks for poisonous gas.
A stray shell from returning government fire risks hitting a chemical plant about six miles away in separatist-controlled territory. The plant, one of Europe’s largest fertilizer factories, has pressurized tanks and more than 12 miles of pipelines holding poisonous ammonia gas.
An explosion there could produce a toxic cloud that could serve as an excuse for a Russian invasion or, American officials have warned, Russia could stage its own explosion there to justify intervention.
Another potential flash point in the area, a water network that supplies drinking water to several million people on both sides of the conflict, may have been damaged by shelling on Saturday. Russia’s Interfax news agency cited a spokesman for the self-proclaimed Donetsk People’s Republic saying that shelling had struck a pumping station and the water supply was at risk.
A loss of water for residents in the Russian-backed areas would reinforce Russian assertions of dire conditions for civilians and would be a setback for Ukraine, which has tried to persuade residents that the government is not their enemy. A cutoff of that water supply amid fighting in 2014 hastened a flow of refugees from the city.