ABIDJAN, Ivory Coast – The United Nations said Sunday it has received hundreds of reports of people being abducted from their homes at night by armed assailants in military uniform and that there is growing evidence of "massive violations of human rights" since Ivory Coast's disputed election.

The statement from the U.N. High Commissioner for Human Rights came a day after the U.N. said it would remain in Ivory Coast despite demands from the man refusing to give up the presidency that thousands of peacekeepers get out of the West African country.

Navi Pillay, the top U.N. human rights official, said Sunday that more than 50 people have been killed over the past three days in Ivory Coast; previous estimates were that up to 30 people had died in the violence.

The deteriorating security conditions in the country and the interference with freedom of movement of U.N. personnel have made it difficult to investigate the large number of human rights violations reported," Pillay said in a statement released from her office in Geneva.

It also said that the armed assailants behind the home abductions had been "accompanied by elements of the Defense and Security Forces or militia groups.

International pressure is mounting for Laurent Gbagbo to concede defeat to opposition leader Alassane Ouattara, whose victory has been recognized by the United Nations, the United States, former colonizer France and the African Union.

In Washington, the U.S. State Department on Sunday ordered most of its personnel to leave Ivory Coast because of the deteriorating security situation and growing anti-Western sentiment.

The order issued Sunday exempts only the State Department's emergency personnel. U.S. officials also warned all American citizens to avoid travel to the West African nation until further notice.

The EU was giving Gbagbo until Sunday to concede defeat or face sanctions that would include an assets freeze and a visa ban on him and his wife. The U.N. Security Council is also expected to meet Monday to discuss Ivory Coast's political crisis.

Still, experts say there are few strong options for forcing Gbagbo out of office, and it is unlikely the African Union or others would back a military intervention.

The trouble is both sides are clearly preparing now for conflict, and a cornered Gbagbo shows little sense of the national tragedy unfolding through his brinkmanship," said Alex Vines, head of the Africa program at Chatham House, an independent research center in London.

Vines said it was more likely that the African Union would seek a "soft landing" for Gbagbo, though it remained unclear whether he would consider such an exile offer.

In a statement read on state television Saturday, Gbagbo's spokeswoman said that 9,000 U.N. peacekeepers and another 900 French troops supporting them were to leave the volatile West African country immediately. Gbagbo accused the U.N. mission of backing his opponent, Alassane Ouattara, and arming rebels who support him.

The U.N. and the international community recognize Ouattara as the victor of last month's presidential runoff vote. The U.N. had been invited by the country itself to supervise the vote and certify the outcome following a peace accord after Ivory Coast's 2002-2003 civil war.

About 800 U.N. peacekeepers are protecting the compound from which Ouattara is trying to govern the country. They are in turn encircled by Gbagbo's troops.

The U.N. secretary-general said late Saturday that the U.N. mission known as UNOCI would stay in Ivory Coast despite Gbagbo's demand.

UNOCI will fulfill its mandate and will continue to monitor and document any human rights violations, incitement to hatred and violence, or attacks on U.N. peacekeepers," said a statement released by a spokesperson for U.N. Secretary-General Ban Ki-moon.

The U.N. Security Council on Monday also planned to discuss the renewal of UNOCI's mandate, which is due to expire on Dec. 31.

While the U.N. peacekeepers plan to continue their work, Gbagbo's demand raised fears that U.N. personnel and other foreigners could be targeted in violence. Over the weekend, masked gunmen opened fire on the U.N. compound. Two military observers were wounded in a separate incident.

Fighting between security forces and Ouattara's supporters already has left as many as 30 people dead.

On Saturday, the chairman of the West African regional bloc ECOWAS said the group supported sanctions against Gbagbo.

We still will explore any other avenue for changing government or making Gbagbo yield power to Alassane Ouattara", chairman James Victor Gbeho said without further elaborating during a visit to Burkina Faso.

The European Union said it would impose an assets freeze and a visa ban on Gbagbo and his wife after the Sunday deadline elapsed. The United States is also prepared to impose targeted sanctions on Gbagbo, his immediate family and his inner circle.

Sanctions, though, have typically failed to reverse illegal power grabs in Africa in the past.

On Thursday, Ouattara called on his supporters to seize key institutions, leading to deadly street clashes. Police and troops loyal to Gbagbo prevented Ouattara's supporters from marching on government buildings Friday.

Ivory Coast was once an economic hub because of its role as the world's top cocoa producer. The civil war split the country in 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.

National identity remains at the heart of the divide. The question of who would even be allowed to vote in this long-awaited election took years to settle as officials tried to differentiate between Ivorians with roots in neighboring countries and foreigners.

Ouattara had himself been prevented from running in previous elections after accusations that he was not Ivorian, and that he was of Burkinabe origin.

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Associated Press Writer Brahima Ouedraogo in Ouagadougou, Burkina Faso contributed to this report.