A blast rocked a secret FSB training base near Simferopol, capital of the Russian-annexed peninsula of Crimea.
The site is reportedly used by Russian border guards, part of the Federal Security Service [FSB] and crucial to Vladimir Putin’s illegal control of a region seen as Ukrainian under international law.
A picture shows black smoke rising from the facility near Skilne, and a short distance from Simferopol airport.
Mikhail Razvozhaev, the Putin-appointed governor of Sevastopol, also in Crimea, claimed that “loud noises heard in the city are preventive training exercises” at the facility.
The mysterious blast at the FSB facility was on Tuesday.
A subsequent fire in fields around the facility was said by Russian sources to have been unrelated to the blast.
However there were also suspicions that the FSB outpost could have been hit by a Ukrainian drone or a sabotage attack as Kyiv gears up a counteroffensive in the war with Russia.
Chp Sevastopol Telegram channel reported a loud explosion near Gogol Street, as well as “over the city” and “somewhere from the city centre”.
Ukraine rarely claims responsibility for strikes on Russian or Russian-controlled territory.
The FSB was once headed by Putin, a former KGB spy.
It comes after Russia launched its second large salvo of missiles at Ukraine in recent days early Monday, damaging buildings, killing two people and wounding 40 in the eastern city of Pavlohrad but failing to hit Kyiv, officials said.
Air raid sirens began blaring across the capital about 3.45am, followed by explosions as Ukrainian defense systems intercepted missiles.
Eighteen cruise missiles were fired from the Murmansk and Caspian regions, and 15 of them were intercepted, said Ukrainian Armed Forces Commander-in-Chief Valerii Zaluzhnyi.
The head of Kyiv's city administration, Serhii Popko, said all missiles fired at the city were shot down, as well as some drones. He didn't provide further details.
The attack follows Friday's launch of more than 20 cruise missiles and two explosive drones at Ukraine, the first to target Kyiv in nearly two months.
In that attack, Russian missiles hit an apartment building in Uman, a city about 215 kilometers (135 miles) south of Kyiv, killing 21 people, including three children.
In Monday's attack, missiles hit Pavlohrad, in the eastern Dnipropetrovsk region, killing two people and wounding 40, Ukrainian President Volodymyr Zelensky said.
Seven missiles were shot at the city and "some were intercepted" but others struck an industrial facility, sparking a fire, authorities said. Damage was reported to 24 apartment buildings, 89 homes, six schools and five shops, according to regional authorities.
Missiles also hit three other areas in the Dnipropetrovsk region, damaging residential buildings and a school, said Serhii Lysak, the region's top official.
Russian Defense Ministry spokesman Igor Konashenkov said Monday that Russia conducted "a group missile strike with long-range precision-guided airborne and seaborne weapons on facilities of Ukraine's defense industry ... all designated facilities were struck."
A Russian-installed official in the occupied Zaporizhzhia region, Vladimir Rogov, said the attack hit ammunition and fuel depots in Pavlohrad, which he said would impede Ukraine's planned counteroffensive.
