KRAMATORSK, Ukraine — A national guard soldier in Ukraine opened fire on Thursday at a missile and rocket factory in the eastern part of the country, killing five people, the police said.
While details of the shooting were scarce and there was no immediate sign that it was related to the military buildup in the region, it underscored the dangers of the moment as fears of a Russian attack on Ukraine grow by the day.
The gunman fled the scene, leading to a sprawling manhunt that lasted for hours before a suspect was taken into custody, according to the police. The police identified the man as Artemiy Ryabchuk and said he was born in 2001, but released few other details about him.
Even as the investigation proceeded, the episode was caught in the murkiness of a broader geopolitical struggle between the West and Russia, in which the Kremlin is trying to reduce the Western presence in a region that it considers within its sphere of influence. U.S. officials have warned that Russia could employ disinformation, paramilitary attacks and sabotage.
This month, the United States said, Russia had dispatched intelligence agents and saboteurs into eastern Ukraine to stage a provocation, with the region’s industrial infrastructure seen as a potential target.
The site of the shooting early on Thursday morning — commonly known as Yuzhmash, an aerospace and rocket factory that American officials have long viewed as posing a risk of weapons proliferation — is precisely the kind of strategic location that Western officials are watching intensely.
They worry that Russia might point to any sign of instability inside Ukraine as a pretext for a military intervention. Jen Psaki, the White House press secretary, said this month that the United States believed Russia was potentially seeking to manufacture events that it could cite as a reason to invade, “including through sabotage.”
The shooting took place in Dnipro, one of the largest cities in the country and more than 100 miles from the frontline of the war in eastern Ukraine, where the Ukrainian military has been fighting Russian-backed separatists since 2014.
Given that the factory was once a production site for intercontinental ballistic missiles, it was tightly guarded even before the latest tensions.
The police said that shortly before 4 a.m., as soldiers were collecting their weapons in a guard house, the gunman opened fire. There were 22 people in the room at the time, the authorities said.
Four of those killed were fellow soldiers. An employee of the factory was also killed, the police said. Five other people were wounded.
A statement from Ukraine’s Interior Ministry, which oversees the police, said that the soldier had turned his weapon on fellow service members who were guarding the plant, and then fled.
The statement said the soldier had fired “for undetermined reasons.”
Later, Denys Monastyrsky, Ukraine’s interior minister, wrote in a post on Facebook that the police were examining the suspect’s medical records since the time of his enlistment, suggesting that the investigation would include the possibility of a psychological disorder.
The attack came only hours after the United States and NATO provided written responses to Russian demands over Western nations’ presence in former Soviet states, saying some security issues could be discussed while others were nonnegotiable.