LONDON—The U.S. dollar is set to break a two-day losing streak on Thursday, while the Japanese yen gained, after a Russian news report of mortar fire in eastern Ukraine jangled market nerves and boosted safe haven bets. While the greenback retreated from highs in Asia after the news broke, investors remained wary that Russia will attack Ukraine, burnishing the dollar’s safe haven appeal despite optimism at the start of this week that a diplomatic solution would be found to prevent conflict. Against a basket of its rivals, the dollar steadied at 95.751 after rising above 96 in early Asian trading. It fell to a Feb. 11 low in the previous session. Russia-backed rebels accused Ukrainian forces of shelling their territory in violation of agreements aimed at ending conflict in the contested Donbass area, the RIA news agency said, a report denied by Ukraine. But in a sign that markets were …