ABIDJAN, Ivory Coast - The United States approved travel sanctions on Laurent Gbagbo and 30 of his allies Tuesday as pressure mounted on the incumbent leader to step down following last month's presidential election that the international community says he lost.

Meanwhile, the U.N. refugee agency said that about 6,200 people already had fled the West African country's postelection violence, and regional leaders called on Gbagbo to "yield power with dignity without further delay."

The rebuke from neighboring nations carries added weight because Gbagbo's representatives have dismissed similar calls from former colonizer France and other Western nations as foreign interference.

The regional bloc, ECOWAS, also said Gbagbo's weekend demand that thousands of U.N. peacekeepers leave the volatile country "would further heighten tensions and worsen the plight of the vulnerable."

The United Nations has certified Alassane Ouattara as the winner of the Nov. 28 vote, and Gbagbo on Saturday ordered the nearly 9,000 U.N. peacekeepers to leave immediately. The United Nations has refused to do so, and a Security Council resolution adopted unanimously Monday extended the force's mandate until June 30, 2011.

U.N. Secretary-General Ban Ki-moon warned Tuesday that Ivory Coast faces "a real risk" of return to civil war.

He said the U.N. peacekeeping force in Ivory Coast has "confirmed that mercenaries, including freelance former combatants from Liberia, have been recruited to target certain groups in the population."

He said that forces loyal to Gbagbo are also obstructing the movement of U.N. personnel and their operations and called on member states to do what they can to supply the U.N. mission.

Secretary of State Hillary Rodham Clinton has authorized travel sanctions against members of Gbagbo's government, a U.S. official said Tuesday.

William Fitzgerald, the U.S. deputy assistant secretary for African affairs, said the move initially concerns about 30 people, though he could not give their names, in accordance with U.S. law. He said the travel sanctions take effect immediately.

The children and close family members of Gbagbo backers can also be deported from the United States, for example if they are studying or interning there, he said. A senior adviser to Gbagbo confirmed earlier this month that Gbagbo's stepdaughters - the children of the first lady - are believed to be living in the Atlanta area.