In a move that further cements Russia's control over parts of eastern Ukraine, Russian officials announced Tuesday they will begin supplying electricity to separatist-controlled areas after the Ukrainian government cut off power because of a heavy backlog of unpaid bills.

Kremlin spokesman Dmitry Peskov described the decision as a humanitarian mission helping to keep an estimated 3 million people out of darkness in rebel-held areas in the Luhansk region along Russia's border. The rebels are backed by Russia.

Ukraine on Monday announced it would stop supplying power because of mounting debts, and power was cut off shortly before midnight.

"Cutting the power supply to the Luhansk region is yet another step by Ukraine to push those territories away," Peskov told reporters in Moscow, saying the move "contradicts the spirit" of the peace accords that Kiev and the rebels signed in Minsk, Belarus, under Russia and European mediation in 2015.

Despite the three years of fighting in eastern Ukraine that has killed more than 9,900 people, trade and supplies of water and electricity for the most part have continued across the front line. Many factories and coal mines in this industrial heartland are interdependent, and a rupture in supply lines could cause a complete industrial breakdown.

The decision on electricity "falls into the trend of Ukraine shutting off Luhansk and Donetsk, and Donetsk shutting off Ukraine and moving closer to Russia," said Alexei Makarkin at the Moscow-based Center for Political Technologies. "The Minsk agreements are not working, and each side waits for the other to get too weak to stand up for its interests."

Georgiy Tuka, Ukraine's deputy minister for the occupied territories, blamed the separatists in the Luhansk and Donetsk regions for accumulating 11 billion hryvnias ($431 million) in unpaid debt for power supplies. Tuka said Kiev was not worried about the consequences of cutting power to large swathes of land because it expected Russia to step in.

Russia has been propping up the Donetsk and Luhansk separatists since the conflict began in April 2014, although the Kremlin has denied sending troops or weapons. The war began after Russia annexed Ukraine's Crimean Peninsula on the Black Sea in 2014, securing its large military marine base.

Boris Gryzlov, the Russian envoy mediating talks between the separatists and the Ukrainian government, said the separatists could not pay for the Ukrainian electricity because Kiev made it impossible to wire money from those territories into the rest of Ukraine. He said Russia would start supplying power to the area.

Separatist officials, speaking on Russian state television, said power was restored after 40 minutes thanks to local sources of electricity. They said Luhansk on Tuesday was getting electricity from two power plants on separatist-controlled territory in the Donetsk region. They also listed Russia as a source of electricity, but it was unclear whether those supplies had begun.

Despite Russia's recent decisions to recognize separatist travel documents and supply electricity, Moscow has shown no inclination to annex those territories. The instability and uncertain status of Donetsk and Luhansk give Russia a degree of leverage over the Ukrainian government in Kiev, which is eager to align closer with the West.

After Russia failed to get Ukraine to recognize separatist authorities, it was left with two choices: abandon eastern Ukraine or provide even more support, Makarkin said. What the Kremlin appears to be doing is similar to how it has been supporting separatist forces in Moldova's Trans-Dniester: "On the official level, you recognize it to be Ukraine's territory but actually it isn't so."

The Ukrainian ombudsman for human rights, Valeria Lutkovska, criticized the government's decision to cut off the power in Luhansk, saying it would further alienate people living in separatist-held areas from the central government in Kiev.