WASHINGTON - The United States is urging African nations to help boost the numbers of U.N. peacekeeping troops already stationed in the Ivory Coast to prevent the country from sliding into a new civil war, the State Department said Wednesday.

Washington is also considering financial sanctions against recalcitrant President Laurent Gbagbo, spokesman Philip J. Crowley said. Gbagbo has refused to step down after an election that the United Nations has said he lost.

Gbagbo's defeat was "irrefutable" and he must step down, Crowley told reporters.

In Paris, World Bank President Robert Zoellick said Wednesday that the bank had frozen loans to the Ivory Coast. The Central Bank of West African States also has halted lending, Zoellick said.

Opposition leaders in the West African nation, the world's top cocoa producer, called for the international community to use force to oust the president.

The U.N. Security Council has rejected Gbagbo's demand for the 9,105-member international peacekeeping mission to leave the country.

France, the former colonial power in the Ivory Coast, and the United States are talking to Nigeria and other countries about augmenting the U.N. peacekeeping force, Crowley said. There is no discussion of U.S. forces playing a role, he said.

The United States is concerned that Gbagbo "may challenge the presence of that force through force of his own," Crowley said. "We want to make sure that the U.N. has the capability to maintain peace and stability."

Crowley said that while the United States "would hope that the use of force would not be necessary" to oust the president, buttressing troops would "send a clear message" that he must leave office.

Violence has broken out since Ivory Coast's Electoral Commission, backed by the United Nations, declared Alassane Ouattara winner over Gbagbo in the Nov. 28 presidential runoff.

Ouattara and Gbagbo both took the oath of office on Dec. 4, and confrontations have followed almost daily since then, leaving at least 50 people dead and 200 injured, according to the United Nations.

On Tuesday, the State Department announced it has imposed travel sanctions against Gbagbo and 30 of his allies. William Fitzgerald, U.S. deputy assistant secretary for African affairs, said trade sanctions also were possible against the individuals.

A 2002-03 civil war killed hundreds and displaced a million people. The United Nations sent peacekeepers to the country in 2004 to monitor the cease-fire, and the country was officially reunited in a 2007 peace pact.