Ban Ki-moon said the incumbent, Laurent Gbagbo, was illegally trying to expel the UN's peacekeeping force after it recognised Alassane Ouattara as victor.
Earlier, an ally of Mr Gbagbo warned the peacekeepers that they could be treated as rebels if they did not go.
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Hide AdAnd in his first TV address since the poll Mr Gbagbo stressed his legitimacy.
He also offered to let a panel representing international powers examine the results of the election.
Mr Gbagbo said Mr Ouattara could leave the Golf Hotel in Abidjan, where he has set up his headquarters, protected by the UN.
The army meanwhile announced the lifting of a nightly curfew, so families could "enjoy the end of year holidays and the New Year".
In a speech to the UN General Assembly on Tuesday, Mr Ban said he was worried about the 10,000-strong mission in Ivory Coast (Unoci).
His offer of a panel to solve the crisis came as a surprise at the end of his speech.
Spain agrees austerity budget
Spain's parliament passed an austerity budget for 2011 by a wafer-thin margin of 177-171, saving embattled Prime Minister Jose Luis Rodriguez Zapatero his job. It also gave him a victory in his bid to convince markets that the nation would avoid a Greek-style financial bailout.
India missile test success
India successfully tested a short-range, nuclear-capable missile with a range of 220 miles today, an official said.
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Hide AdThe army twice fired the surface-to-surface missile Prithvi II from a range in Chandipur in the eastern state of Orissa, said SP Dash, an official at the range.
"The test was successful," the official said.
The missile, which would target mainly military installations, can carry a warhead weighing up to 1,100lb he said.
BrahMos - as a deterrent against neighbours China and Pakistan.
India's Agni-II missile, with a range of up to 1,250 miles, can put areas of southern China within striking distance. And the Agni-III, successfully tested last year, can carry nuclear warheads across much of Asia and the Middle East.
Vatican clarifies condom stance
The Vatican has clarified recent comments by Pope Benedict XVI on condoms, saying he did not mean they could be used to avoid pregnancy.
The Congregation of the Doctrine of the Faith said the Pope said condoms could reduce the risk of HIV infection in certain cases, such as for a male prostitute.
Boy aged 9 is chess master
A nine-year-old boy has become the youngest chess master in the United States.
Samuel Sevian, of California, earned the title after a match in San Francisco this month, after which the US Chess Federation gave him a rating of 2,201. A rating of 2,200 makes a player a master.
A Christmas message for North Korea
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Hide AdSouth Korea: Officials lit a massive steel Christmas tree overlooking the border as troops stood guard and a choir sang carols, in a defiant message to the atheist North.
The ceremony was a sign that the administration is serious about countering the North's aggression.
United States: Barack Obama secured enough Republican votes to ratify a new arms control treaty with Russia that will cap the former foes' nuclear warheads.