MOSCOW - Russia and Ukraine sank further into a widening trade war on 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 peninsula of Crimea, which Russia annexed in March 2014 but which still depends on Ukraine for much of its key infrastructure.

Following a 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."

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

"Supplies are being stopped until new payments arrive from the Ukrainian company," he said.

Russia briefly cut gas supplies to Ukraine in July and in June 2014 as Russian-backed separatists and Ukrainian forces clashed in the country's southeast, following the ouster of former 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.

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.