MOSCOW — As funerals were held Monday for five nuclear workers 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.

Radiation levels in Severodvinsk rose by up to 16 times on Aug. 8 after an accident that authorities said involved a rocket test, state news agencies reported. (Reuters)

The explosion of liquid rocket fuel, on a platform in Dvinsky Bay, threw several of those who died into the water, reported the Russian nuclear agency, Ros­atom. 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 already had 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.

President Trump tweeted Monday that the United States is “learning much from the failed missile explosion. We have similar, though more advanced, technology.”

Also Monday, Valentin Kostyukov, director of the center in Sarov, said on local television that researchers from the institute had been working at the northern test site for a year. Rosatom’s chief, Alexei Likhachev, said work on the new weapon would continue, without specifying what that weapon is.

Sarov, a closed town about 250 miles east of Moscow that has been a center of nuclear research since 1946, was rocked by news of the accident in the far north.

Sergei Kirienko, first deputy chief of staff to Putin, attended the funeral, as did the governor of the region and the chiefs of the nuclear program. Kirienko said the dead workers would be given posthumous state awards.

“They are heroes of contemporary Russia,” Kostyukov said.

“There’s a brotherhood” at the institute, said Alexander Chernishev, deputy scientific director of the center. In planning for the risks associated with the missile tests, he said, “I must say, what happened was not foreseen.”

Speaking at the outdoor funeral, the flower-draped coffins, Kirienko said: “They took a double responsibility: In addition to developing unique technologies and unique products, they took the physical risk of conducting the tests, in which, unfortunately, no matter how much you calculate in advance, no matter how much you prepare, it is impossible to eliminate the risk 100 percent. They as professionals knew this very well, but they took this risk, understanding that no one could do it better than them.”

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.

Monday also marked the 19th anniversary of the sinking of the Kursk, a Russian nuclear-powered submarine. All 118 personnel aboard died after the vessel settled on the bottom, as the Russian navy refused foreign offers of help. Putin, newly elected as president, came under heavy criticism for continuing a vacation; this was at a time when the Russian press was still boisterous and unfettered. The day was marked in Severodvinsk and other ports of Russia’s Northern Fleet.