Heraldo de Madrid - Ukraine strike kills 3 in Russian-occupied Crimea

US Secretary of State Marco Rubio warned of a "real" risk of the Ukraine war escalating as Kyiv underlines its ability to strike deep inside Russian territory with the attacks.

Ukraine has described its strikes on Saint Petersburg as "fair" retaliation for a wave of Russian bombardment on its territory.

Sergey Aksyonov, the Moscow-installed head of the Crimea region, said early Thursday that preliminary reports showed a strike on non-residential buildings in Simferopol claimed three lives and wounded seven others.

"Emergency services are currently at the scene," Aksyonov wrote on Telegram.

The strike came as 20,000 people from 130 countries were due at the three-day annual Saint Petersburg International Economic Forum (SPIEF) -- an event once dubbed "Russia's Davos".

President Vladimir Putin is to give a keynote address at the forum on Friday and Kremlin spokesman Dmitry Peskov vowed Russia would provide a "systemic" response to Ukraine's strikes on the city.

Black smoke from the strikes was visible from the conference venue as the first sessions started on Wednesday.

Valeria, a 32-year-old businesswoman from Moscow at the forum, told AFP she was used to the threat of attacks.

"We have been living under such attacks for many years now," she said.

- 'Real' escalation risk -

Ukrainian officials have said the Saint Petersburg attack on an oil terminal and the city's Kronstadt military base was meant to disrupt the conference.

"The Petersburg forum is opening with a nice plume of black smoke in the background after Ukrainian strikes," said Sergiy Sternenko, an adviser to the Ukrainian defence minister.

Ukrainian President Volodymyr Zelensky said his country was responding "accordingly" to Russian bombardment.

"It's just a matter of time before we can scale up the intensity of our responses," Zelensky said during a press conference in Kyiv with NATO chief Mark Rutte.

On Wednesday, a drone strike on a bus in Russian-occupied east Ukraine killed at least seven people, Moscow-installed officials said.

Two others were killed, one in the Bryansk region near the Ukraine border and another in the Russian-occupied Kharkiv region, they added.

Meanwhile, Russian attacks left at least 10 dead across Ukraine, local officials said.

Rubio said at a US Senate appropriations panel that Ukraine has "become increasingly effective at conducting long-range strikes deep into Russia".

It's "one of the things that reminds us of why it's important to try to bring this war to an end, if we can, because the risk of escalation is real, more real than it was two years ago," Rubio added.

Speaking earlier to the House Foreign Affairs Committee, Rubio lamented the lack of progress on ending the war, which began with Russia's full-scale invasion in February 2022.

"To this point, neither side has been willing to make concessions, particularly on the Russian side, necessary in order to bring peace about," he said.

"But we stand ready, and we've engaged and invested a tremendous amount of high-level time on that conflict over the last year," he added.

EU foreign affairs chief Kaja Kallas earlier told AFP that Ukraine's attacks had spooked the Kremlin.

"Putin is losing money, men, and momentum, and that's why he's increasing attacks on civilians."

H.Santana--HdM