Ukrainian drones have again damaged Russia’s Baltic Sea port of Ust-Luga, the governor of the local region said on Tuesday, potentially adding to Russia’s difficulties in exporting oil.

Kyiv has stepped up attacks on Russia’s oil export infrastructure over the past month, launching its heaviest drone strikes of the more than four-year war against the Baltic ports of Ust-Luga and Primorsk.

At least 40% of Russia’s oil export capacity has been halted due to drone attacks, a disputed strike on a major pipeline and the seizure of tankers, according to Reuters calculations based on market data.

Leningrad Governor Alexander Drozdenko said three people, including two children, were treated for injuries and several buildings were damaged in the overnight attacks.

In a message on Telegram at 0409 GMT, he said air-raid alerts in the region had been lifted but gave no details on damage to the port.

Ust-Luga, on the south-eastern shore of the Gulf of Finland, is a sprawling complex of oil-processing facilities and export terminals handling crude oil and oil products.

According to source-based data, the port exported 32.9 million metric tons of oil products last year. It typically handles about 700,000 barrels of crude oil per day.

Authorities say Ust-Luga was hit on March 22, 25, 27, 29 and 31, forcing suspensions of export operations.

Ukrainian President Volodymyr Zelenskiy said on Monday that some of Ukraine’s allies had sent Kyiv “signals” about the possibility of scaling back its long-range strikes on Russia’s oil sector as global energy prices have surged.