The United Nations Security Council has demanded an immediate end to the escalating violence in Ivory Coast and imposed sanctions on Laurent Gbagbo, who has refused to relinquish the presidency, and his inner circle.

Last night's security council vote was unanimous and came five days after France and Nigeria introduced a draft resolution expressing "grave concern" that the west African nation could relapse into civil war.

"I think the sense of urgency is obvious since ... the confrontation is extending in Ivory Coast and the situation is worsening by the hour," France's UN ambassador Gerard Araud said. The message "is very simple - Gbagbo must go. It is the only way to avoid a full-fledged civil war".

The UN's most powerful body voted on the day that fighters supporting Ivory Coast's internationally recognised president, Alassane Ouattara, seized control of the country's administrative capital Yamoussoukro.

It was seen as a symbolic victory by Mr Ouattara's forces after months of political chaos that began when Gbagbo, the incumbent president, refused to recognise the results of the November election.

The resolution demanded "an immediate end to the violence" and urged all Ivorian parties "to respect the will of the people and the election" of Mr Ouattara as president.

It condemned Gbagbo's decision not to accept the solution proposed by a high-level African Union panel earlier this month, which includes recognising Mr Ouattara as president, and urged him step aside immediately.

The African Union had also suggested getting Mr Ouattara to appoint members of Gbagbo's political party to a unity government. Mr Ouattara said he had embraced this idea since last year's presidential campaign, but Gbagbo rejected it.

The resolution backs the African Union proposal and calls for "an overall political solution that preserves democracy and peace and promotes lasting reconciliation among Ivorians".

Ivory Coast, the world's largest cocoa producer, has been in turmoil for almost a decade.

It was split into a rebel-controlled north and government-controlled south after an attempted coup sparked civil war in 2002.

A peace deal in March 2007 brought key rebel leaders into the administration and offered hope for a single government after years of foundering accords and disarmament plans. But the results of the November 29 presidential election made clear that deep divisions remain.

UN sanctions on Ivory Coast, including an arms embargo and controls on the export of rough diamonds, have been in effect since 2004.

To step up pressure, the latest resolution slapped a travel ban and asset freeze on Gbagbo, his wife Simone, and three key supporters, Desire Tagro, Pascal Affi N'Guessan, and Alcide Djedje.

The resolution was the most robust since the crisis over the presidency, though the council didn't impose tough financial or trade sanctions.

US ambassador Susan Rice said the resolution sent a strong signal "both of council unity and the international community's determination that the people of Ivory Coast once and for all have the opportunity to see a government by the people installed".

Ivory Coast's UN ambassador Youssoufou Bamba, who represents Mr Ouattara, called the council action "a strong, robust response" to the worsening violence in his country.

The resolution reiterates the security council's long-standing demand that Gbagbo "without delay" lift the siege of the Golf Hotel, where Mr Ouattara is trapped, protected by UN peacekeepers.

The security council also targeted forces loyal to Gbagbo who have used mortars to fire on civilians in the capital Abidjan.

At least 25 people were killed on March 17 when Gbagbo loyalists fired several mortar shells at a market building in the rebel-held Abobo district of Abidjan.

Gbagbo's forces earlier used heavy machine guns against women demonstrating peacefully in support of Mr Ouattara in Abobo on March 3, killing seven and seriously wounding many others.

Nigeria's UN ambassador U Joy Ogwu said the timing of the vote was critical, coming amid troubling reports that the growing violence was taking on ethnic and sectarian overtones and that innocent civilians, especially women and children were being targeted.

The resolution called on all parties to fully co-operate with an investigation of alleged rights abuses in Ivory Coast by the UN Human Rights Council's independent international commission.

The initial draft's call for the commission's report to be sent to the prosecutor at the International Criminal Court was dropped. Instead, the resolution calls for the report to be sent to the security council "and other relevant international organisations".

The International Criminal Court's prosecutor, Luis Moreno-Ocampo, is already conducting a preliminary examination of possible war crimes and crimes against humanity in Ivory Coast.