Asian shares slumped on Friday, after flaring Ukraine tensions spoiled investor risk appetite and bolstered the safe-haven yen. Ukraine’s president said Russian troops had entered his country in support of pro-Moscow rebels who captured a key coastal town, escalating a five-month-old separatist conflict. The United States on Thursday openly accused Russia of sending combat forces into Ukraine and threatened to tighten economic sanctions, but Washington stopped short of calling Moscow’s latest step an invasion.