|UN soldiers have been told to do what is necessary to defend themselves and Ouattara [EPA]
Laurent Gbagbo, Cote d'Ivoire's incumbent leader has accused world leaders of launching a coup to oust him.
Giving a new year address on state television, on Friday, Gbagbo said that he would not cede power to Alassane Ouattara, who is internationally recognised as having won November's election.
A senior Ouattara spokesman said that the country is in a "civil war" situation.
Ouattara is under UN protection in Cote Golf hotel in Abidjan.
In Gbagbo's new year address, he has called for his rival to leave the hotel. And some of Gbagbo's supporters have given Ouattara till January 1 to come out.
Gbagbo said he does not want war, "Tonight, on the eve of the New Year, I would like to launch another appeal to all the personalities who are still in the Golf Hotel. I am asking them to go back to their homes. The time for war has gone. Now it's the moment for dialogue."
West African regional military chiefs have prepared plans to "forcefully take over power" from Laurent Gbagbo, the incumbent Cote d'Ivoire president, should eleventh hour diplomatic efforts to persuade him to step down fail, a Nigerian defence spokesman said on Friday.
The plan was established during meetings of military chiefs from the Economic Community of West African States (ECOWAS) in Abuja, the Nigerian capital, earlier this week.
"The committee of chiefs of defence staff met on Tuesday and Wednesday to put machinery in motion that if all political persuasions fail ... ECOWAS will forcefully take over power from Laurent Gbagbo and hand over to Alassane Ouattara," Colonel Mohamed Yerimah told the AFP news agency.
Yerimah said the military option was a "last resort", and that "hopefully Gbagbo will be persuaded to hand over power politically".
The meetings were attended by military chiefs from Benin, Burkina Faso, Ghana, Liberia, Mali, Senegal, Togo, Niger and Nigeria.
The UN General Assembly last week recognised Ouattara as the winner of a disputed November 28 presidential run-off poll. However, Gbagbo has also claimed victory and remains in control of key state institutions, including the army and the media.
A delegation of three West African presidents met Gbagbo in the southern Ivorian city of Abidjan on Tuesday to deliver an ultimatum to either step down or face the use of force. They have given him until January 3, the date of their next meeting with Gbagbo, to respond.
ECOWAS has a standby troubleshooting force of 6,500 soldiers, which officials have said could be ready to deploy by mid-January.
A meeting to fine-tune the logistics of any operation is scheduled for January 17 and 18 in Mali, Yerimah said. That meeting will finalise when troops would be deployed and how long they could remain in the country.
Yerimah said the group's 12 active member countries will be expected to contribute troops and materials for the operation.
The UK on Friday said that it would support any UN bid to use force to oust Gbagbo, but stopped short of committing troops to a military intervention. It also announced that it no longer recognised Philippe D Djangone-Bi, a Gbagbo-appointee, as the Ivorian ambassador to the United Kingdom.
'Civil war' threat
"[Gbagbo] should not underestimate the determination of the international community that the will of the people of that country should be recognised and a democratic transfer of power take place," William Hague, the British foreign minister, told BBC Radio.
|Gbagbo supporters have been urged to take hold of Ouattara's headquarters [EPA]
"We have deployed a military liaison officer to the country to work on various contingencies with the French, but I'm not raising the possibility today of British forces being deployed."
The country appears to be edging towards more unrest, however, as Gbagbo's notorious 'street general' and minister for youth and employment, Charles Ble Goude, called on Gbagbo supporters to seize control of Ouattara's headquarters in the Golf Hotel in Abidjan on Jan 1.
The UN warned on Friday that such a move could plunge the world's largest cocoa producer back into civil war. Ban Ki-Moon, the UN secretary general, said that UN forces at the Golf Hotel are authorised to use all means necessary to protect themselves and Ouattara.
The United Nations' High Commissioner for Human Rights said on Friday that she has written to Gbagbo and other senior Ivorian officials to make it clear that they could be held criminally accountable for human rights violations.
Navi Pillay, a former UN war crimes judge, said that the international criminal justice system had been developed to the point where heads of states and other actors could "no longer ... be sure that they can commit atrocious violations and get away with it".
The UN has also said that armed men, apparently loyal to Gbagbo, have been preventing staff in the country from investigating a building where up to 80 bodies are believed to have been kept in a "mass grave".
Ouattara sets deadline
On Friday, Ouattara's prime minister Guillaume Soro gave incumbent president Gbagbo until midnight on Dec 31 to leave office. He said that if Gbagbo quits before the start of the new year, he will "have no worries".
Soro also said the country is in a "civil war situation".
"This is what's at stake: Either we assist in the installation of democracy in Ivory Coast or we stand by indifferent and allow democracy to be assassinated," he said told reporters at a news conference.