Tensions between Moscow and Kiev ratched up further today as Ukraine decided to stop buying gas from Russia and closed its airspace to its giant eastern neighbour's airlines.
The two measures not only underscore the acrimonious nature of the former Soviet 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".
A shaky Ukrainian truce is being increasingly put to the test as Russia steps up its air campaign in support of President Bashar al-Assad in Syria.
The Ukrainian military said another soldier was killed in a new bout of clashes across the shattered war zone in the past 24 hours.
The army also said it had imposed a unilateral ceasefire as of midnight in a bid to calm the violence.
But Ukrainian soldiers "will not watch calmly if the enemy decides to attack our positions," the Ukrainian military's General Staff said in a statement.
"In case their lives are in danger, our servicemen - as previously - have the right to open fire."
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 and plunged Moscow's relations with the West to a post-Cold War low.
