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 fellow soldiers and wounding five others, the police said, a new security concern at a time when there are fears of a Russian incursion.
A statement from Ukraine’s Ministry of Interior, which oversees the police, said the soldier had turned his weapon on fellow service members who were guarding the Southern Machine Building Plant, and then he fled.
The statement said the soldier had fired “for undetermined reasons.” The police and national guard were searching for the suspect, the ministry said. The soldier and those shot were not immediately identified.
There was no immediate indication of a connection between the shooting and the military tensions around Ukraine. Russia has amassed tens of thousands of troops near Ukraine’s borders and demanded security guarantees from the United States and NATO.
The factory, located in Dnipro, one of the largest cities in the country, is more than 100 miles from the frontline in the war in eastern Ukraine but is tightly guarded. It was once a production site for intercontinental ballistic missiles.
The attack at the factory, about 4 a.m. Thursday, came hours after the United States and NATO provided written responses to Russian demands, saying some security issues could be discussed while others were nonnegotiable.
Ukrainian and Western officials have been on alert for actions that could be destabilizing for the Ukrainian government or provide justification for a Russian military incursion.
Earlier 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 company that now operates the factory makes civilian rockets for satellite launches and has cooperated with the National Aeronautics and Space Administration on designs for resupply missions to the International Space Station. Its rocket models include the Anteres, the Cyclone and the Zenit, but it has struggled to remain relevant and profitable in the international space launch industry
The rocket factory, often known by its shortened name Yuzhmash, was a focus of United States concerns about the proliferation of missile technology to rogue states such as North Korea.
For Russia, the factory’s separation during the Soviet breakup from what had been an integrated space and military industry was seen as emblematic of the economic and scientific disruptions caused by Ukraine’s emergence as an independent country.
This month, the White House accused Moscow of sending saboteurs into eastern Ukraine to stage an incident that could provide President Vladimir V. Putin of Russia a pretext for ordering an invasion of the country. The administration did not release details of the evidence it had collected, but Jen Psaki, the White House press secretary, had said the operatives were trained in urban warfare and explosives.
“Russia is laying the groundwork to have the option of fabricating a pretext for invasion,” Ms. Psaki said, “including through sabotage activities and information operations, by accusing Ukraine of preparing an imminent attack against Russian forces in eastern Ukraine.”