Ukraine on Wednesday banned all Russian airlines from crossing its airspace, the latest escalation between the two neighbours 19 months into a separatist war in the east of the former Soviet state.
The announcement by Kiev's pro-Western government came only moments after Russia said it was once again halting gas shipments to energy-dependent Ukraine starting Thursday.
The two measures not only underscore the acrimonious nature of the countries' relations but also highlight how difficult one of Europe's deadliest crises since the Balkans Wars of the 1990s may be to resolve.
Ukrainian Prime Minister Arseniy Yatsenyuk told a televised cabinet meeting that the flight ban was justified because "Russia might use Ukrainian airspace to stage provocations".
"This is an issue of our country's national security - a response to the Russian Federation and its aggressive actions." Ukraine and its Western allies accuse Moscow of orchestrating and supporting the pro-Russian revolt in the east to avenge last year's ouster of Kiev's Kremlin-backed president and the new government's decision to align itself with the West.
Kiev on October 25 barred most Russian airlines from flying into Ukraine - a decision that prompted immediate reciprocal measures by Moscow.
But President Petro Poroshenko's government had at the time allowed Russian airlines to cross Ukrainian airspace to other destinations.
Yatsenyuk said the new decision came "in part as result of the escalation of the military and geopolitical situation".
As Russia steps up its air campaign in support of President Bashar al-Assad in Syria, a shaky truce in eastern Ukraine is also being increasingly put to the test.
The Ukrainian military said another soldier was killed in a new bout of clashes across the shattered war zone in the past 24 hours.
"Military activities have intensified," Ukraine's National Security and Defence Council said in a statement.
Some analysts and politicians in Kiev accuse Russian President Vladimir Putin of using the world's focus on his campaign in Syria as cover for launching a new phase in the Ukrainian war.
Russia denies all involvement in a conflict that has killed more than 8,000 people, mostly civilians, and plunged Moscow's relations with the West to a post-Cold War low.
Moscow has banned the import of most Western food products in response to sanctions imposed over its annexation of the Crimea peninsula from Ukraine last year.
It has also restricted imports of many Ukrainian goods and is threatening a complete embargo on food imports from its neighbour to the west should Kiev joined a planned free trade alliance with the European Union on January 1.
Russia's natural gas giant Gazprom had earlier Wednesday said it would stop shipping fuel supplies to Ukraine because Kiev had failed to make the required pre-payments on time.
Gazprom boss Alexei Miller said Ukraine's state energy firm Naftogaz had used up all the gas it had paid for and "no new upfront payment has been made".
The disruption is the second of its kind this year. Ukraine had already gone a full summer without making any purchases of Russian gas.
Putin waded further into the dispute by pointing the finger of blame at the authorities in Ukraine for the ongoing power disruptions in Crimea.
Nearly two million people in the strategic Black Sea peninsula have been without electricity - almost all of it supplied by Ukraine - since the weekend after its four main pylons were blown up.
The disruption came during attempts by Crimea's ethnic minority Tatars and Ukrainian nationalists to blockade the region and prompt its forced return to the mainland.
No one has claimed formal responsibility for the Crimean power outage.