Ukraine has said it attacked naval targets and port infrastructure in Crimea, in one of its biggest strikes on the Russian navy's Black Sea fleet.
Russia earlier claimed Ukraine had launched 10 missiles and three unmanned boats in the attack.
It caused a large fire at a Sevastopol shipyard which left 24 people injured, Russia said.
The Moscow-installed governor claimed most of the weapons were intercepted but that two ships had been damaged.
Ukraine has strongly implied western-supplied cruise missiles were used in the attack, one of the biggest on the Black Sea fleet since the war started.
Unmanned vessels, known by many different names including sea drones and drone boats, operate on or below the water. They usually have built-in explosives and cameras that feed directly back to the person controlling them.
A photo shared by Sevastopol Governor Mikhail Razvozhayev on Telegram shows flames engulfing what appears to be a ship at a port as he stands speaking into his phone.
It is thought to be in an area where ships were undergoing repairs.
A large landing ship, named the Minsk, and a submarine, called the Rostov-on-Don – both thought to be in dry dock – are said to have been damaged. This makes it one of Ukraine's most significant attacks so far on the Black Sea fleet.
According to state-run Ria Novosti news agency, the Russian defence ministry said both vessels will be fully repaired and continue in normal service.
Ukrainian military intelligence official Andriy Yusov told Reuters: "We confirm a large landing vessel and submarine were hit. We do not comment on the means (used) for the strike."
In a post on Telegram, the head of Ukraine's air force Mykola Oleshchuk thanked his pilots for their "excellent combat work" – strongly suggesting weaponry had been launched by Ukrainian aircraft. He also warned there was more to come.
Posted in Ukrainian, Mr Oleshchuk used language which strongly implied the use of either UK Storm Shadow or French SCALP cruise missiles. These missiles have a range of over 150 miles (240km) – triple the range of missiles Ukraine used previously.
When contacted, the air force said Storm Shadow and SCALP cruise missiles are the only such weapons currently in Ukrainian use.
This appears to be the first time such weapons have been used on targets inside Crimea.
Images circulating on social media, which the BBC has yet to verify, show several large explosions in the area.
The fact that some missiles got through Russia's air defences and appear to have done substantial damage will be of real concern in Moscow.
Seven of the missiles were downed and all three unmanned boats were destroyed, the country's defence ministry claimed.
Russia illegally annexed Crimea from Ukraine in 2014 and this attack shows the tussle for control of the waters.
Ukraine has consistently maintained that its ultimate goal is to retake the peninsula and it is not the first time it has targeted Sevastopol and the Black Sea fleet.
Meanwhile, Russian drones reportedly damaged the Ukrainian grain port of Izmail, on the Danube river.
The governor of the Odesa region, Oleh Kiper, said six people had been injured in the attack, which caused a fire and damaged infrastructure.
"Several groups of drones were launched at the Izmail district," Mr Kiper said on Telegram.
"Unfortunately, there were hits: damage to port and other civil infrastructure was recorded."
In recent days, Ukraine claimed it seized back control of four gas drilling platforms in the northern Black Sea, close to the Crimean peninsula. The so-called Boyko Towers were captured by Russia in 2015, shortly after its annexation of Crimea.
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