U.S. President Barack Obama has welcomed the candidacy of U.N. Secretary-General Ban Ki-moon for a second term heading the world body.

In a statement Tuesday, the White House said Mr. Ban has made important reforms and led the U.N. as it played a critical role in crises and challenges around the world — including in Haiti, Ivory Coast, Libya and South Sudan.

The White House described the U.N. as an “imperfect, but indispensable institution” and called for further efforts at reform to improve effectiveness, streamline bureaucracy and reduce costs.

Mr. Ban formally announced his candidacy for a second five-year term Monday.

The 66-year-old former South Korean foreign minister said he had sent a letter to the 192 U.N. member states to “humbly” offer himself for re-election. Mr. Ban has been secretary-general since January 1, 2007, and his term ends on December 31.

His bid has the backing of the United States and other key members of the U.N. Security Council, and he appears almost certain to be re-elected.

Diplomats say Mr. Ban is expected to run unopposed and the Security Council will likely recommend he be reconfirmed. The U.N. General Assembly could then hold a formal vote before the end of June.