By Karin Strohecker and Megan Davies LONDON/NEW YORK (Reuters) -The U.S. government broadened restrictions on trading of Russian government debt on Tuesday in a bid to punish Moscow for ratcheting up its conflict with Ukraine, a move that analysts said might have a moderate impact near-term but could be a step toward harsher measures. The U.S. Treasury said it was prohibiting participation in the secondary market for bonds issued after March 1. The increased restrictions on dealings in Russia’s sovereign debt are aimed at “further cutting Russia off from sources of revenue to fund its governme…