A rocket engine explosion on a naval test range in northern Russia has killed two people and injured six, the defence ministry told Russian media.
The victims of the explosion in Arkhangelsk region were civilian specialists while military and civilian personnel are among the injured.
The ministry said radiation levels were normal but the city of Severodvinsk registered a "brief spike" in levels.
An area of the White Sea nearby has reportedly been closed for a month.
But the deputy head of Archangelsk port, Sergei Kozub, told the BBC the closure was planned before the accident.
Radiation levels peaked between 11:50 and 12:30 (08:50-09:30 GMT) before falling and normalising by 14:00, the city administration in Severodvinsk said on its website, without reporting how significant the spike had been.
It is unclear what could have caused radiation levels to rise.
Local people were reportedly urged to take precautions against radiation. No increase in ambulance call-outs was recorded, the administration added.
A woman in Severodvinsk named only Alina told Russian news site lenta.ru: "I work in the hospital where they're bringing the injured.
"They advise everyone to close their windows and drink iodine, 44 drops per glass of water."
Children in local kindergartens were taken indoors after reports of the blast and parents were advised not to take them outside in the evening, other residents were quoted as saying.
What do we know about the explosion?
The defence ministry did not say officially where or when the blast occurred but unofficial sources say it happened near the village of Nyonoksa, where a navy missile test range is located.
Nyonoksa is about 47km (29 miles) west of Severodvinsk, which has a population of nearly 200,000 and is 1,260km from the Russian capital, Moscow.
"During testing of a liquid jet engine an explosion and combustion of the product occurred," the ministry said in a statement.
"There have been no harmful chemicals released into the atmosphere, the radiation levels are normal."
Emergency aircraft were used to airlift the injured. They included defence ministry officials and developer company representatives, who "had injuries of varying severity", the statement added.
There had been earlier reports of a fire at a military facility near Nyonoksa. Telegram-based media outlet Mash said radiation levels in the village were three times higher than normal.
Nyonoksa carries out tests for virtually every missile system used by the Russian navy, including sea-launched intercontinental ballistic missiles, cruise missiles and anti-aircraft missiles.
It is the second accident involving Russia's military this week.
On Monday, one person was killed and eight others were injured in a blaze at an ammunition dump in Siberia.
Flying munitions damaged a school and a kindergarten in the area. More than 9,500 people were evacuated.
An investigation is under way into the cause of the incident.