She said restrictions imposed on U.N. personnel in the West African nation have made it "impossible" to investigate all the allegations about serious human rights violations - including reports of mass graves. At least 90 people have been tortured or treated inhumanely, and there have been 24 cases of disappearances.

David Kennedy, spokesman for the U.S. mission to the U.N. in Geneva, said the United States is "deeply concerned by the extent of the abuses being perpetrated" in Ivory Coast.

The U.N. and other world leaders recognize Alassane Ouattara as the winner of the Nov. 28 runoff vote. His prime minister has urged the U.N., European Union, African Union and others to consider intervening to push incumbent Laurent Gbagbo out of the presidency.

The United States said Wednesday it is discussing ways to help quell the postelection violence in Ivory Coast with other countries.

"We are in discussions with other regional countries to see if there are ways in which we can reinforce the U.N. peacekeeping force," spokesman P.J. Crowley told reporters. "It could be that that kind of reinforcement could be another way to send a clear message to President Gbagbo."

He declined to name the countries that have been contacted but noted that Nigeria is a major troop contributor to West African peacekeeping forces and that France has interests in Ivory Coast, a former French colony where at least 13,000 French citizens reside.

A Nigerian military spokesman said Thursday that military intervention into another country could only be decided by the president, and a presidential spokesman could not be reached for comment. The regional bloc ECOWAS is due to hold a meeting on the crisis late Friday.

Still, there has been little international interest so far in a military intervention in Ivory Coast, which suffered a 2002-2003 civil war. The United States and the EU are imposing sanctions targeting Gbagbo, his wife and political allies. Hundreds of U.N. peacekeepers have been protecting the hotel where Ouattara is based.

Over the weekend, Gbagbo ordered all U.N. peacekeepers out of the country immediately in an escalation of tensions. The U.N. considers Ouattara president and is staying put, raising fears that U.N. personnel and other foreigners could be targeted in violence as tensions mount.

The U.S. State Department has ordered most of its personnel to leave because of the deteriorating security situation and growing anti-Western sentiment, and France and Germany also have recommended that their citizens leave.

Financial pressure is also being increased on Gbagbo in an effort to force him out. On Wednesday, the World Bank confirmed that it has frozen loans to the country. The bank's aid commitment to Ivory Coast was $841.9 million as of January 2010, according to the bank's website.

Ouattara has also sought to use financial pressure to force Gbagbo out, appealing to the West African central bank (BCEAO) to cut off his access to state coffers, making it impossible to pay civil servants and soldiers. Such a move could set the stage for mass defections and turn the tide against Gbagbo.

Ivory Coast was once an economic hub because of its role as the world's top cocoa producer. The 2002-2003 civil war split the country into a rebel-controlled north and a loyalist south. While the country officially reunited in a 2007 peace deal, Ouattara still draws his support from the northern half of the country where he was born while Gbagbo's power base is in the south.

Gbagbo claimed victory in the presidential election only after his allies threw out half a million ballots from Ouattara strongholds in the north, a move that infuriated residents there who have long felt they are treated as foreigners in their own country by southerners.

While Ouattara has received the support of the international community, Gbagbo still controls the military and state media, the main source of news in a country where international television and radio have been blocked since the election dispute began.