Russia has been forced to suspend shipping in the Sea of Azov after 90 vessels were targeted by Ukrainian drones in less than a week.

Ukraine’s drone forces chief, Robert Brovdi, said on Sunday that his units had hit 10 tankers and four ferries overnight, as well as a major oil refinery in the city of Syzran. There were multiple strikes on electricity sub-stations in occupied Crimea, he added.

“The technological humiliation of the [Russian] empire continues. It will fall because of Crimea,” Brovdi wrote on social media. He said Moscow’s shadow fleet, which transports sanctioned oil products around the world, was “noticeably shrinking” and could no longer use the Kerch strait, connecting the Sea of Azov with the Black Sea.

The Sea of Azov is a vital waterway that connects Russia with eastern Europe. It is of crucial economic and military importance to Moscow, which uses it to ship oil, grain and other products such as steel to international markets.

Russia suspended shipping through the Don-Azov canal on Friday, Reuters reported. The canal connects with a Russian river network and the Caspian Sea. This export route via Kerch and the Bosphorus strait in Turkey is effectively shut down.

Ukraine’s former defence minister, Andriy Zagorodnyuk, said the Kremlin had lost control of a “critical” maritime corridor. He said the blockade affected military vessels and shipping transporting grain stolen from occupied southern Ukraine and moved through the ports of Berdyansk and Mariupol.

“The Caspian Sea doesn’t have any connection to the world’s oceans. It has turned into a lake. All of its products – agricultural, fertiliser, whatever – go through this channel and river,” Zagorodnyuk said.

Russia’s small flotilla in the Caspian was likewise trapped, he added, predicting further strikes on Russian ships in and around the Black Sea port of Novorossiysk.

Ukraine has been systematically destroying much of Russia’s radar and anti-aircraft defences. This has enabled it to carry out a series of devastating long-range strikes on Russian oil refineries, including one last week in the Siberian city of Omsk, 2,700km (1,700 miles) from Ukrainian territory.

Residents in Syzran reported the sound of drones at 5am on Sunday followed by loud explosions. Photographs and videos showed a large fire at the oil refinery, with thick columns of black smoke rising above an industrial area. The complex supplies the Russian military and sends fuel abroad via the Azov-Kerch canal.

Kyiv has also launched a wave of mid-range strikes on land and sea supply routes into occupied Crimea, hitting lorries, ships and crossing points. One tanker caught fire overnight as it entered the Azov-Black Sea canal, Russian officials said. On Sunday, local channels reported two large oil spills off the coast of Taganrog.

Yevgeniya Gaber, a senior fellow at the Atlantic Council thinktank, said the attacks were part of a much broader strategy that included isolating Crimea and “turning it into an island”.

The overall goal was “to progressively degrade Russia’s ability to sustain offensive operations by disrupting logistics, fuel supplies and transport infrastructure, and cutting off military units in the south of Ukraine”, she said.

Gaber added: “There is not a single oil refinery that is unhit now. Maritime logistics in the Sea of Azov, all of this fits into the same strategy and operational concept, which is a strategic neutralisation of Russia. I’m sure we will see more deep strikes on Russian territory.”

Video released by Brovdi’s unmanned strike aviation brigade, Magyar’s Birds, shows Russian tankers fitted with protective cages and ropes. These have not prevented night-time Ukrainian drone strikes and crews have abandoned some damaged and burnt-out vessels, leaving them adrift.

Repeated Ukrainian attacks have forced the authorities in Crimea to declare a state of emergency. Widespread electricity blackouts and acute petrol shortages have been reported and the peninsula’s tourist industry has collapsed. Car drivers have been forced to travel to Russia in search of fuel, with long queues outside petrol stations in many regions.

Volodymyr Zelenskyy, Ukraine’s president, has described the strikes on Russia’s energy infrastructure as part of Kyiv’s campaign of “long-range sanctions” carried out in response to Moscow’s refusal to end its war. Vladimir Putin insists his original military goals – to seize the eastern Donbas and other Ukrainian regions – are unchanged.

Overnight, three people were killed in Russian attacks on Ukraine’s central Dnipropetrovsk region, including two in a bombing of an industrial facility in Zelenskyy’s home city of Kryvyi Rih, regional officials said. A separate drone attack on the southern city of Kherson killed a 48-year-old, reported its mayor, Yaroslav Shanko.