The owner of the Russian Wagner Group private military contractor actively involved in the fighting in Ukraine has predicted that the war could drag on for years.

Yevgeny Prigozhin said in a video interview released late Friday that it could take 18 months to two years for Russia to fully secure control of Ukraine's eastern industrial heartland of Donbas. He added that the war could go on for three years if Moscow decides to capture broader territories east of the Dnieper River.

The statement from Prigozhin, a millionaire who has close links to Russian President Vladimir Putin and was dubbed “Putin’s chef” for his lucrative Kremlin catering contracts, marked a recognition of the difficulties that the Kremlin has faced in the campaign, which it initially expected to wrap up within weeks when Russian troops invaded Ukraine on Feb. 24.

Russia suffered a series of humiliating setbacks in the fall when the Ukrainian military launched successful counteroffensives to reclaim broad swaths of territory in the east and the south. The Kremlin has avoided making forecasts on how long the fighting could continue, saying that what it called the “special military operation” will continue until its goals are fulfilled.

The Russian forces have focused on Ukraine’s Luhansk and Donetsk provinces that make up the Donbas region where Moscow-backed separatists have been fighting Ukrainian forces since 2014.

Ukrainian and Western officials have warned that Russia could launch a new broad offensive to try to turn the tide of the conflict as the war approaches the one-year mark. But Ukraine's military intelligence spokesman, Andriy Chernyak, told Kyiv Post that “Russian command does not have enough resources for large-scale offensive actions.”

“The main goal of Russian troops remains to achieve at least some tactical success in eastern Ukraine,” he said.

Prigozhin said that the Wagner Group mercenaries were continuing fierce battles for control of the Ukrainian stronghold of Bakhmut in the Donetsk region. He acknowledged that the Ukrainian troops were mounting fierce resistance.

As Russian troops have pushed their attacks in the Donbas, Moscow has also sought to demoralize Ukrainians by leaving them without heat and water in the bitter winter.

On Friday, Russia launched the 14th round of massive strikes on Ukrainian energy facilities and other vital infrastructure. High-voltage infrastructure facilities were hit in the eastern, western and southern regions, resulting in power outages in some areas.

Ukraine's energy company, Ukrenergo, said Saturday that the situation was “difficult but controllable,” adding that involved backups to keep up power supplies but noting that power rationing will continue in some areas. Head of Ukraine's state nuclear operator Energoatom Petro Kotin said Saturday that more power will come into the country's energy system after two nuclear reactors have been repaired.

Ukraine's military chief, Gen. Valerii Zaluzhnyi, said that Russian forces launched 71 cruise missiles, 35 S-300 missiles and seven Shahed drones between late Thursday and midday Friday, adding that Ukrainian air defenses downed 61 cruise missiles and five drones.

The Ukrainian authorities reported more attacks by killer drones later on Friday. The Ukrainian air force said the military downed 20 Shahed drones in the evening.

Russia's Defense Ministry said that Friday's strikes hit all the designated targets, halting the operation of Ukraine's defense factories and blocking the delivery of supplies of Western weapons and ammunition. The claim couldn't be independently verified.

Late Friday, Russian military bloggers and some Ukrainian news outlets posted a video showing an attack by a sea drone on a strategic railway bridge in the Odesa region. The grainy video showed a fast-moving object on the surface of the water approaching the bridge in Zatoka, about 50 kilometers (30 miles) southwest of Odesa, and exploding in a powerful blast.

The authenticity of the video couldn't be verified, but the Ukrainian military on Saturday confirmed the use of sea drones by Russian forces.

Ukraine’s military chief Zaluzhnyi said in an online statement that he has expressed concern about the use of such drones in a phone conversation with the U.S. Chairman of the Joint Chiefs of Staff, Gen. Mark Milley, on Saturday, adding that it “poses a threat to civilian navigation in the Black Sea.”

The attack marks the first combat use of a sea drone by Russia in the conflict. Igor Korotchenko, a retired colonel of the Russian armed forces who frequently comments on the conflict on Russian state TV, noted Saturday that such drones should be equipped with a more powerful load of explosives to inflict more significant damage.

The bridge, which was targeted by Russian missile strikes early in the war, serves the railway link to Romania, which is a key conduit for Western arms supplies.

In other developments, the governor of Russia's Kursk region along the border with Ukraine said that a group of construction workers was hit by Ukrainian shelling that killed one of them and wounded another.

The governor of another Russian border region, Belgorod, reported the shelling of the town of Shebekino, saying it damaged two buildings but no one was hurt.