Ukraine has carried out a strike on the outskirts of Russia's St Petersburg, hours before the opening of a major economic forum designed to attract foreign investment into the country.

As dawn broke black plumes of smoke rose over Russia's second city, where Vladimir Putin is due to address the financial event on Friday. Thousands of guests from 130 countries are due to attend, including a low-key US delegation.

Local authorities said air defences shot down 59 drones overnight and that three different districts of St Petersburg had been hit, although no one was killed.

Kremlin spokesman Dmitry Peskov said Moscow would respond to the strikes. "Our responses will be systemic in nature," he said on Wednesday.

Mobile internet was disrupted and St Petersburg's Pulkovo Airport was temporarily closed, while some regions of nearby Latvia and Estonia also issued air raid alerts.

Hours later, Volodymyr Zelensky confirmed Ukrainian drones had hit several locations in Russia, including the oil terminal and a naval base in the nearby town of Kronstadt.

"The Ukrainian plan of long-range sanctions is being implemented exactly as it is needed to bring peace closer," Zelensky wrote on social media, using a euphemism for long-distance strikes on Russia.

0:20 Drone strike hits Russian oil depot in St Petersburg area

Kronstadt is the main outpost of the Russian Navy's Baltic Fleet. Unverified videos posted on social media by Ukrainian military figures showed drones heading for docked military ships, with the video cutting off before impact.

Robert Brovdi, the commander of Ukraine's unmanned systems, said on Telegram that the corvette Boikiy was struck.

The St Petersburg Economic Forum - once dubbed the "Russian Davos" - is a flagship event on the Russian political agenda.

Until Moscow launched its full-scale invasion of Ukraine in 2022, it used to be attended by high-profile Western delegations, including CEOs and heads of state.

This year, for the first time in nearly a decade, a low-key US delegation is also due to participate in the forum. It is led by the head of the US Commission of Fine Arts Rodney Mims Cook Jr, the official who has been overseeing President Donald Trump's ballroom project at the White House.

US right-wing commentator Candace Owens and Putin-backing US actor Steven Seagal are also due to attend.

In a tongue-in-cheek post on X, Denys Shtilierman of Ukrainian defence company Fire Point said: "Due to such distinguished guests and the importance of the event itself, we couldn't ignore it - and urgently flew to [St Petersburg]."

The post was accompanied by videos of drones crossing the sky and thick black smoke billowing from undisclosed locations on the sea front.

In the four years since Russia's invasion began, Ukraine has developed a booming defence sector. Kyiv is now able to regularly hit targets within Russia, focusing its efforts on energy infrastructure and oil facilities, which it sees as fuelling the Russian war machine.

On Wednesday, seven people were killed after a drone hit a passenger bus travelling in the Russia-controlled Donestk region of Ukraine, a Moscow-installed official said.

Moscow, meanwhile, continues to strike Ukrainian cities, resulting in regular civilian casualties. On Monday night alone, at least 22 people were killed in combined missile and drone strikes across Ukraine.