Russian-backed authorities in the occupied region of Crimea in Ukraine say at least four people have been killed in the latest wave of Ukrainian strikes on the peninsula.

Three people were killed and seven wounded in one of the attacks on what were described as "non-residential facilities" in the regional capital, Simferopol. It appears to be the first attack resulting in fatalities there.

In a separate incident, one person was killed and three injured in an attack on a commuter train travelling to the city of Kerch, the Russia-installed Crimea leader said.

Ukraine has not commented. It marks the third day in a row it has been accused of targeting civilian transport in its occupied territories.

Kyiv has recently expanded its attacks inside Russia, too.

On Wednesday, it carried out a strike on the outskirts of St Petersburg, hours before the opening of a major economic forum designed to attract foreign investment into the country.

According to President Volodymyr Zelensky, Ukrainian drones had hit several locations in Russia, including the oil terminal and a naval base in the nearby town of Kronstadt - the main outpost of the Russian Navy's Baltic Fleet.

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 delegation, including heads of state.

Russian President Vladimir Putin ordered the occupation of Crimea in 2014.

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, eight people were killed after a drone hit a passenger bus travelling in the Russia-controlled Donetsk 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.