The Ukrainian military says it has "successfully" struck the headquarters of Russia's Black Sea fleet in occupied Crimea in an attack using Storm Shadow and SCALP cruise missiles.
Such weapons have been supplied by the UK and France to Ukraine in its fight against Russia's invasion.
British Storm Shadow missiles were also used in an attack on 13 September against the HQ, where a Russian submarine and warship were damaged in a barrage on a shipyard in the port city of Sevastopol.
In the latest assault, the navy building caught fire after being hit by a missile, according to Moscow and its allies.
One serviceman was missing following the attack, said the Russian defence ministry which earlier stated he had been killed.
The city's Russian-installed governor, Mikhail Razvozhayev, said the strike caused a fire and no one was injured outside the building but he did not talk about any other casualties.
Firefighters battled the blaze and more emergency forces were being brought in - a sign of the large scale of the fire.
A stream of ambulances arrived at the building and shrapnel was scattered around an area of hundreds of metres, the Tass news agency reported, adding police asked residents to leave the city centre, where the naval HQ is located.
Mr Razvozhayev initially told Sevastopol residents that another attack was possible and urged them not to leave buildings or go into the centre.
He later said there was no longer any threat of an airstrike but reiterated that people should not go to the central part of the city.
The defence ministry said five missiles were shot down by its air defence systems responding to the Sevastopol attack.
It was not immediately clear if the HQ was hit in a direct strike or by debris from an intercepted missile.
The missile attack comes a day after five people were killed when Russian missiles and artillery pounded cities across Ukraine.
US to supply Ukraine with long-range missiles
Meanwhile, President Biden has told his Ukrainian counterpart President Zelenskyy that the US will provide a small number of long-range missiles, Sky News understands.
Ukraine has for months asked for the Army Tactical Missile System (ATACMS) which would give Kyiv the ability to strike targets from up to 180 miles away, hitting supply lines, railways and command and control locations behind the Russian frontlines.
It is not known when the missiles will be delivered.
Mr Zelenskyy met Mr Biden and congressional leaders in Washington on Thursday.
Mr Biden has been pressing Congress to approve an extra aid package for Ukraine worth $24bn (£19.5bn) amid Russia's ongoing invasion.
Crimea has also been struck by an "unprecedented" cyberattack in the wake of the missile strike, according to an official.
"An unprecedented cyberattack on Crimean internet providers," noted Oleg Kryuchkov, an adviser to the Russian governor of the region, on Telegram.
"We are detecting interruptions in the internet on the peninsula," he added. "All services are working to eliminate the threat."
The outage has not been verified and it was not clear what could have caused it.
The Crimean Peninsula was annexed from Ukraine by Russia in 2014 in an act that most of the world saw as illegal.