Lukoil, Russia’s largest private oil company and one of the few to voice opposition to the Kremlin’s war in Ukraine, says its chairman has died following a “serious illness,” disputing local media reports that he had plunged to his death from a hospital window.

“We deeply regret to announce that Ravil Maganov … passed away following a serious illness,” Lukoil said in a statement on September 1, hours after local media quoted sources and unnamed law enforcement officials as saying the 67-year-old fell out of the window of the Central Clinical Hospital in the Russian capital and died.

The state-controlled TASS news agency cited an unnamed law enforcement source as saying Maganov had committed suicide by jumping from a sixth-story window after being admitted to the hospital for a heart attack. The news site RBK also said police were investigating the possibility of suicide.

Maganov had worked for Lukoil since the early 1990s and was considered a Kremlin loyalist.

However, Lukoil raised eyebrows in March — just weeks after Russia invaded Ukraine — as one of the only companies to condemn the war, calling it “tragic” while urging for the “earliest [possible] end to the armed conflict.”

The Lukoil statement on Thursday gave no further details on Maganov in what is the latest in a series of mysterious deaths of Russian businessmen since Moscow launched its unprovoked invasion of Ukraine on February 24.

In May, Russian media reported that a former top manager of Lukoil, Aleksandr Subbotin, was found dead in a basement in a house in the town of Mytishchi near Moscow.

According to the sources, the owner of the house where the billionaire’s body was found, Aleksei Pindyurin, also known as Shaman Magua, testified to police that Subbotin came to his house under the influence of alcohol and drugs seeking a ritual he often asked Pindyurin to perform to relieve hangover symptoms.

Weeks before that, Vagit Alekperov, the founder and co-owner of Lukoil, resigned after he and other Russian tycoons were hit by sanctions by Australia and the United Kingdom over Moscow’s invasion of Ukraine.

The same day, media reports said a former top manager at Russian gas giant Novatek, Sergei Protosenya, his wife, and daughter, had been found dead in a rented villa in the town of Lloret de Mar near Barcelona.

Several other senior Russian businessmen and their families have also been found dead amid unclear circumstances.