TOKYO—The Bank of Japan kept monetary policy steady on Wednesday but offered a bleaker view on exports and factory output, as Asian factory shutdowns caused supply-chain disruptions for some manufacturers. As widely expected, the BOJ maintained its short-term interest rate target at—0.1  percent and that for 10-year government bond yields around zero percent. “Exports and factory output continue to increase, although they are partly affected by supply constraints,” the central bank said in a statement announcing its policy decision. In July, the BOJ said exports and output continue to increase steadily.