TOKYO — The Bank of Japan kept monetary policy on hold and gave a brighter assessment of the economy on Tuesday, encouraged by a rebound in factory output and increasing signs that the recovery from the devastating March earthquake is broadening.

But the central bank warned that emerging nations faced a tough balancing act between curbing inflation and sustaining economic growth.

It also reiterated that U.S. balance sheet adjustments and Europe’s debt woes were among risks to Japan’s economic outlook, in light of a series of weak U.S. economic data, which increased concerns that exports may get less support from global demand just when Japan is overcoming supply chain problems from the March 11 earthquake and tsunami.

As widely expected, the Bank of Japan kept its benchmark interest rate steady at a range of zero to 0.1 percent by a unanimous vote and held off on loosening monetary policy further.