Exhaust fumes rise from a Ukrainian heating plant in Kiev on Nov. 25, 2015. The head of Russia’s state-run natural gas export monopoly, Gazprom, said Wednesday it was cutting off supplies to Ukraine. (Roman Pilipey/European Pressphoto Agency)

Russia and Ukraine sank further into a widening trade war Wednesday, as Russia halted all gas deliveries to Ukraine and Ukraine banned Russian airlines from transiting over its airspace.

Tensions have heightened over the disputed Crimean Peninsula, which Russia annexed in March 2014 but which still depends on Ukraine for much of its key infrastructure.

After a power blackout in Crimea prompted by an explosion that downed several electricity pylons on Ukrainian territory, the two countries have traded punitive measures with little restraint.

Russian President Vladimir Putin told journalists Wednesday that Ukraine’s government had tacitly supported the Crimea blackout, which he said was “torturing people.”

A worker at a Ukrainian gas station Volovets in western Ukraine controls a valve. . (Pavlo Palamarchuk /AP)

On Wednesday, the chief executive of the Russian energy giant Gazprom said in a statement that gas supplies to Ukraine would be cut off that day until Russia received prepayment for further deliveries.

“Supplies are being stopped until new payments arrive from the Ukrainian company,” said Alexei Miller, the Gazprom chief.

Russia briefly cut gas supplies to Ukraine in July and in June 2014 as Russian-backed separatists and Ukrainian forces clashed in southeastern Ukraine after the ouster of President Viktor Yanukovych. Russia also cut gas supplies in 2006 and 2008 because of price disputes.

Ukrainian Prime Minister Arseniy Yatsenyuk responded Wednesday by announcing that the national gas company, Naftogaz, had been directed to buy gas from European suppliers, and by introducing a ban against flyovers of Russian aircraft.

“This is an issue of our country’s national security — a response to the Russian Federation and its aggressive actions,” Yatsenyuk said in televised comments at a cabinet meeting. The decision would most directly affect flights from Russia to Moldova and the Balkans, Russian officials said.

Ukraine and Russia already had banned direct flights between the two countries, a decision that affects hundreds of thousands of people and families that are split between the two post-Soviet countries.

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