The U.S. and European Union are stepping up efforts to sway the outcome of the political crisis in Ukraine, putting together a short-term financial aid plan in a move to counter pressure from Moscow.

The prospective aid package, which top U.S. and EU diplomats discussed on the sidelines of a security conference in Munich over the weekend, would be the West's most significant move to date to reopen the geopolitical struggle for Kiev since Ukrainian President Viktor Yanukovych turned his back on an EU economic pact and, instead,...