A series of blasts that rocked a Russian air and naval base in Crimea was the source of speculation on Wednesday, with no official word from Ukraine.
President Volodymyr Zelenskyy used his nightly video address to call for the liberation of the peninsula, which is under Russian occupation, but stopped short of mentioning the blasts.
The Ukrainian Air Force said nine planes were destroyed in the explosions at the Saky airfield, but did not claim responsibility.
"Saky! Minus nine aircraft of the invaders," the Air Force Command wrote on Facebook.
One person was killed and six others injured, Crimea’s Health Department said.
Russia’s Defence Ministry said munitions at the base had exploded, sparking a fire, but insisted that there had been no strike.
Defence analysts, however, said the incident bore the hallmarks of a Ukrainian attack.
Mr Zelenskyy said that Kyiv intended to retake the Crimean Peninsula, which Russia annexed from Ukraine in 2014.
“This Russian war against Ukraine and against the entire free Europe began with Crimea and must end with Crimea — with its liberation,” Mr Zelenskyy said.
"We will never give it up … the Black Sea region cannot be safe while Crimea is occupied."
British Defence Secretary Ben Wallace said it was “clear” explosions at the Russian base were not caused by “someone dropping a cigarette”, as he dismissed Moscow’s “excuses” for the blasts.
Mr Wallace said anyone’s “manual of war” would consider the site on the Crimean Peninsula to be a “legitimate target” for Ukraine to strike.
He said it was “very early days” and the UK would “see what information comes out” about the incident at the Saky air base.
“We’ve pretty much dismissed most of the Russian, I think, excuses — everything from a cigarette butt, I think was one of them, that might have set off two simultaneous large explosions," Mr Wallace told the BBC.
“I think when you just look at the footage of two simultaneous explosions not quite next to each other, and some of the reported damage even by the Russian authorities, I think it’s clear that that’s not something that happens by someone dropping a cigarette.
“First and foremost, Russia has illegally invaded, not just in 2014, but now Ukrainian territory.
“Ukraine, under United Nations articles, is perfectly entitled to defend its territory and take what action it needs to against an invading force.
“So, is it legitimate? It’s absolutely legitimate for Ukraine to take lethal force, if necessary, but take force in order to regain not only its territory, but also to push back its invader.
“And that air force base has been used by Russian air forces to bomb Ukrainian targets. So I think in anybody’s sort of manual of war it would be a legitimate target.”
US defence analyst Chuck Pfarrer tweeted that a weapon called the ATACM, or Army Tactical Missile System, was most likely used to attack the base.
This is a device the US has not yet officially supplied to Ukraine, but which has a range of 300 kilometres.
Others said that Ukrainian Neptune missiles might have been used.
Ukraine already has at least one type of long-range ballistic missile system, the Grіm-2, which has a range of 280km.
An anonymous Ukrainian government official told The Washington Post that Ukrainian special forces had carried out the attack. The official declined to share details on how the raid was conducted.
If confirmed, it would be the first known Ukrainian attack on a Russian military site in Crimea and mark a significant escalation in the war, given that the base is more than 177km from the nearest front line.
The explosion was seen by swimmers and sunbathers at a nearby beach in the village of Novofedorivka, a popular tourist spot. The blast shattered windows in the village and beachgoers were seen scurrying past loungers.
Natalia Lipovaya, a tourist, said she was walking from her car when the blast occurred.
"The earth is gone from under my feet," she told AP.
"I'm standing and it seems to me that I either took off or went underground. I was so scared.
"My husband jumped up. He was resting and said, 'What happened?' And then we were moving away and we immediately saw such a cloud and a column of smoke above us."
Witnesses told Reuters they heard at least 12 explosions about 3.20pm local time on Tuesday from the Saky airbase. They described a final blast about 30 minutes later as the loudest.
Russia annexed the peninsula from Ukraine in 2014 in a move that sparked international outrage.
Russian President Vladimir Putin claimed the move was necessary to protect ethnic Russians living in the region and praised his country's "all-conquering patriotic force".
The group ― the UK, US, Canada, France, Germany, Italy and Japan ― together with the EU, said Ukrainian staff “must be able to carry out their duties”.
Russian troops captured the site, the largest in Europe, during the early days of the invasion of Ukraine and have since controlled it.
Peter Kotin, the head of Ukraine’s nuclear power company, this week told the BBC the Russians were using the plant as a military base to launch attacks against forces loyal to Kyiv.
The G7 and the EU said: “We demand that Russia immediately hand back full control to its rightful sovereign owner, Ukraine, of the Zaporizhzhya nuclear power plant, as well as of all nuclear facilities within Ukraine’s internationally recognised borders to ensure their safe and secure operations".
“Ukrainian staff operating the Zaporizhzhya nuclear power plant must be able to carry out their duties without threats or pressure. It is Russia’s continued control of the plant that endangers the region.”