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MOSCOW — As funerals were held Monday for five nuclear workers who were killed while testing a new missile, Russian officials said they will try to determine what went wrong and how to avoid another such accident in the future.

The weapon prototype they were testing relies on small-scale power sources being developed by the Russian Federal Nuclear Center that use “radioactive materials, including fissile and radioisotope materials,” the scientific director of the center, Vyacheslav Soloviev, said in a video broadcast by a television station in Sarov, where the research institute is based.

“We’re analyzing the whole chain of events to assess both the scale of the accident and to understand its causes,” Soloviev said.

The missile exploded Thursday evening in the Arkhangelsk region in Russia’s far north. Three nuclear workers who were injured have been hospitalized in Moscow.

The explosion of liquid rocket fuel, on a platform in Dvinsky Bay, threw several of those who died into the water, Rosatom, Russia’s nuclear agency, reported. A “short-term” spike in radiation levels was reported Friday by officials in the city of Severodvinsk, near the testing site, but that report was removed from the web later that day. Dvinsky Bay had already been closed to shipping ahead of the missile test, and it will remain so until Sept. 10.

The Serebryanka, a nuclear fuel cargo ship, has been at the test site since last week, according to several reports. Nuclear experts have speculated that it may be recovering radioactive debris from the bottom of the bay.

American and independent Russian observers have suggested that the weapon being tested could have been a nuclear-powered cruise missile, which President Vladimir Putin boasted about last year. The Americans call it the SSC-X-9 Skyfall; Russia has named it the 9M730 Burevestnik. Such a missile, if successfully developed, could fly intricate courses and stay in the air for many hours as it hunted a target.

Last month, a top-secret Russian nuclear submersible was badly damaged in a fire while in the Barents Sea, killing 14 high-ranking naval officers. The Kommersant newspaper reported that a lithium-ion battery may have sparked a fire on the vessel.