Russia has been left furious after its prized flagship Moskva was sunk in the Black Sea, with experts revealing why the destroyed ship is such a blow to President Vladimir Putin. 

Moskva sank on Thursday after an explosion and fire that Ukraine claimed was a successful missile strike, as the Kremlin accused Kyiv of targeting its citizens in sorties across the border. 

Russia's defence ministry has denied Ukraine's claims, instead saying the blast on vessel was the result of exploding ammunition and added that the resulting damage had caused it to "lose its balance" as it was being towed to port. 

"Given the choppy seas, the vessel sank," the Russian state news agency TASS quoted the ministry as saying. 

Regardless of which version of events is correct, the destruction of the Moskva presents Putin with a new problem: How to explain the loss to his citizens. 

An assessment of the situation from the Institute for the Study of War found that both explanations expose a weakness in the Russian military. 

"The Kremlin's current story of losing the flagship of the Black Sea Fleet due to an accidental fire and ammunition explosion will, at minimum, likely hurt Russian morale and cannot be hidden from the Russian domestic audience," the assessment stated. 

"Both explanations for the sinking of the Moskva indicate possible Russian deficiencies — either poor air defences or incredibly lax safety procedures and damage control on the Black Sea Fleet's flagship." 

While the loss of the ship is unlikely "deal a decisive blow" to Russia's operations as a whole, it will impact the country's ability to conduct cruise missile strikes on its enemies. 

Since Russia began its invasion of Ukraine on February 24, Moscow has gone to great lengths to censor the situation and stop its citizens from being able to see what is really happening. 

Russian President Vladimir Putin chairs a Security Council meeting via video conference at the Novo-Ogaryovo residence outside Moscow, Russia. Photo / AP 

Factual inconsistencies and censorship have been reported through the country's state-owned media like Russia Today, Channel One and Sputnik, with jarring discrepancies between casualties and the military's progress in Ukraine. 

While Russia's media landscape offers a mix of state-controlled and independent publications, Moscow has forbidden media to describe the Ukraine invasion as war, opting for the term "special operation" instead. 

Non-government affiliated site The Moscow Times reported last month that "Russia's media watchdog has ordered the country's media to use only official sources" when covering the Ukrainian invasion. 

Those who refuse to comply could be blocked within Russia or fined up to five million roubles, or the equivalent of $66,700. 

In a report from the BBC, packages from Russia's most-watched channels, Rossiya 1 and Channel One also reveal discrepancies. 

In one bulletin, a presenter warns viewers against images of destroyed Russian tanks, calling them "unsophisticated virtual manipulations". 

"Footage continues to be circulated on the internet which cannot be described as anything but fake," they say. 

Nuclear weapons warning after ship sunk 

The US has described the sinking of the Moskva as a "big blow" for the Black Sea fleet, warning it could prompt Putin to escalate the situation. 

Russian Navy missile cruiser Moskva on patrol in the Mediterranean Sea near the Syrian coast. Photo / AP 

The fleet has been blockading the besieged southern port city of Mariupol, where Russian officials say they are in full control. 

Following its pullout from northern Ukraine earlier this month after failing to take the capital, Russia is refocusing on the east, with Kyiv warning of bloody new clashes to come in the Donbas region. 

And with Russian setbacks in the war mounting, the CIA warned that President Vladimir Putin could resort to using a tactical or low-yield nuclear weapon. 

"We're obviously very concerned. I know President Biden is deeply concerned about avoiding a third world war, about avoiding a threshold in which, you know, nuclear conflict becomes possible," CIA director William Burns said in a speech in Atlanta. 

But the United States is yet to see "a lot of practical evidence" of actual deployments that would cause more worry, he added. 

Russian analyst Clint Ehrlich warned Ukraine could expect an "immediate escalation from Moscow" if it really was behind the sinking of the Mosvka. 

"There will be a political imperative for the Kremlin to push this setback from the headlines with positive news," he said. 

"We may see large-scale strategic bombing, something Russia has held back on to date." 

Putin's response to the situation may have already begun, with an air raid alert declared for the entirety of Ukraine in the early hours of Friday morning. 

Media outlet Nexta announced on Twitter yesterday that there had been "an air-raid alert on the entire territory of Ukraine". 

The Kyiv Independent also announced that an air raid alert had been declared "in all of Ukraine's regions at once". 

Ukrainian MP Lesia Vasylenko revealed multiple explosions had occurred in Kyiv, with the ongoing air raid siren already sounding for almost an hour. 

"3 explosions in #Kyiv right now. One after the other," she wrote on Twitter. 

"The air raid warning has been on for an hour. Most likely #put in gone livid because of the #Moskva sinking. Oh well, we'll just keep standing to #Russia's annoyance".