Fears that the crisis in Ukraine is escalating into a new and dangerous phase roiled financial markets Wednesday.

Following allegations of a buildup of Russian troops on the border of Ukraine and the prospect of tit-for-tat sanctions between the West and Moscow, investors have become increasingly vexed by the situation in Ukraine.

The latest jitters, which contributed to a 1.1 percent fall in Japan's Nikkei 225 stock average earlier and a 1.2 percent decline in the Stoxx 50 index of leading European shares, have come in the wake of comments from Polish Prime Minister Donald Tusk that he has information indicating that there is a growing threat of a "direct intervention" by Russia in Ukraine.

Tusk's comments come a day after John Ging, director of U.N. humanitarian operations, warned the Security Council at an emergency meeting requested by Russia that the humanitarian situation in eastern Ukraine is steadily worsening as power and water supplies are scarce, homes are destroyed and health workers flee.

The fear in the markets is that Russia may use these reports of a humanitarian crisis to justify a military incursion, which would clearly ratchet up tensions with the West.

"This is the biggest fear for investors right now and explains why we're seeing more risk aversion in the markets today," said Craig Erlam, market analyst at Alpari.

However realistic these concerns are, investors are also getting vexed by fears that the sanctions imposed on Russia by the European Union and the United States could impact economically on both sides.

Europe stands to lose the most from any escalation given its big trading relationship with Russia. Already, European businesses that have ties with Russia's financial, military and energy sectors stand to lose out from the sanctions.

Even those that don't have direct links to those sanctioned sectors are cautioning over the outlook. German sportswear company Adidas, for example, recently expressed worries over the impact on its business.

So far, European companies appear to be bearing up, though analysts fear it won't take much of an increase in tensions between the West and Russia to start crimping the recovery.

"Loss of export revenues is the most obvious channel, but there may also be damage to business confidence given the heightened uncertainty," James Ashley, chief European economist at RBC Markets.

Russia already appears to be preparing retaliatory sanctions against the EU. On Tuesday, there was widespread speculation that Moscow was preparing measures to close the airspace over Siberia to European flights heading to Asia.