St. Petersburg ¨C Ukrainian drones hit an oil complex and military base in St. Petersburg on Wednesday as ministers and officials gathered for a flagship economic forum in Russia¡¯s second city, officials said.

Ukrainian President Volodymyr Zelenskyy called the strikes ¡°fair¡± retaliation for Russia¡¯s bombardment of Ukraine and threatened more, as his country recovered from Russian drone and missile attacks on Tuesday that killed 23 people.

Some 20,000 people from 130 countries were to attend the three-day annual St. Petersburg International Economic Forum (SPIEF) ¡ª an event once dubbed ¡°Russia¡¯s Davos¡± ¡ª which began Wednesday.

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

The St. Petersburg attacks damaged ¡°several¡± infrastructure facilities, the city¡¯s governor Alexander Beglov said. There were injuries but no fatalities, he added.

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

One man was killed in the Russian region of Briansk near the Ukraine border and another civilian in the Russian-occupied Kharkiv region, officials reported.

Russia¡¯s latest attacks left at least 10 dead across Ukraine, local officials said.

Ukraine said it hit the St. Petersburg Oil Terminal and the city¡¯s Kronstadt military base. Black smoke rose from behind the Peter and Paul Fortress which is among the city¡¯s most popular tourist attractions.

The commander of Ukraine¡¯s drone forces said a Russian warship was hit at the Kronstadt naval base, posting black-and-white drone footage of what he said was the attack.

St. Petersburg¡¯s main airport closed for hours, while several flights from Moscow to the northern capital were delayed.

Ukrainian officials said the attack aimed 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 defense minister.

Smoke was visible from the conference venue as the first sessions started. Valeria, a 32-year-old businesswoman from Moscow at the forum said she was used to the threat of attacks.

¡°We have been living under such attacks for many years now,¡± she said.

During a press conference in Kyiv with NATO chief Mark Rutte, Zelenskyy said Ukraine was responding ¡°accordingly¡± to Russian bombardment.

¡°It¡¯s just a matter of time before we can scale up the intensity of our responses,¡± he said.

Rutte said Ukraine was showing success taking out ¡°some of the key capabilities and capacities of the Russians.¡±

EU foreign affairs chief Kaja Kallas said that Ukraine¡¯s attacks had spooked the Kremlin.

¡°It clearly shows also panic on the Russian side ¡ª why they are increasing...