By Caroline Valetkevitch NEW YORK (Reuters) – U.S. stocks ended sharply lower on Wednesday as Western leaders began gathering in Brussels to plan more measures to pressure Russia to its halt conflict in Ukraine and oil prices jumped. Responding to Western sanctions that have hit Russia’s economy hard, President Vladimir Putin said Moscow will seek payment in roubles for natural gas sales from “unfriendly” countries, while its forces bombed areas of the Ukrainian capital Kyiv a month into their assault. Oil prices jumped 5% to over $121 a barrel and U.S. natural gas futures edged up to a seven-…