A United Nations delegation is in Ivory Coast to deliver a strong message to all sides in the unravelling peace process.
The UN team is expected to put pressure on both sides
They may threaten sanctions, which could include travel bans, diplomatic sources say.
The UN has also said that it will investigate human rights abuses in the period after the rebellion broke out in September 2002.
Ivory Coast is split between rebel- and government-controlled areas.
About 6,000 UN troops will be based in the country by the end of July.
The UN delegation, led by British diplomat Sir Emyr Jones Parry, will hope to capitalise on conciliatory comments made by President Laurent Gbagbo in a televised address on Monday.
The president condemned his supporters' attacks on French and UN targets and he pledged to hold talks with rebels and opposition groups, mediated by the presidents of Nigeria, Ghana and Togo.
Pro-Gbagbo militant groups accuse the international community of backing rebel New Forces who hold northern Ivory Coast.
Former colonial power France has some 4,000 peacekeepers in Ivory Coast and thousands of French citizens remain there, despite attacks on them, which began shortly after the rebellion broke out in September 2002.
"I remind everyone that France is not our enemy. French citizens who live in Ivory Coast are not our enemies. The United Nations is not our enemy," Mr Gbagbo said.
His announcement came after he met the three leaders in the Nigerian capital on Sunday, and came under pressure to seek reconciliation with the rebels.
The threat of UN sanctions, if properly delivered, should get all sides thinking, says the BBC's James Copnall, although Ivorian politicians have heard many warnings from the international community in the last 18 months.
The peace agreement signed in Marcoussis, France in January last year has virtually collapsed amid deepening distrust and animosity between Mr Gbagbo's supporters and the New Forces.
Mr Gbagbo said that the former rebels must disarm before the peace deal can be fully implemented.
The UN High Commission for Human Rights says it will investigate the abuses from 19 September 2002 to 24 January 2003, when a peace deal was signed.
The last UN human rights report, into the suppression of an opposition demonstration in March, caused an uproar in government circles, when it said 120 people had died in a crackdown "carefully planned and executed" by the Ivorian security forces.
Ministers from the New Forces rebel movement were sacked from the transitional power-sharing government in March, after protesting about the security forces' actions.
Gbagbo has come under pressure to revive the stalled peace process
Over the weekend, clashes broke out between rival groups of rebels in the two main northern towns of Bouake and Korhogo.
A New Forces spokesman said 17 attackers and five of their fighters had been killed.
The New Forces claim their leader, Guillaume Soro, escaped an assassination attempt which they blame on Mr Gbagbo and Guinea President Lansana Conte.
A presidential spokesman dismissed the allegations, claiming that the fighting was entirely amongst rival rebel groups.
The factions appear to be split between those loyal to the officially-recognised leader, Mr Soro, and supporters of Ibrahim Coulibaly - a former army sergeant under investigation in France for an alleged plot to kill Mr Gbagbo.
Our correspondent says fighters loyal to leader Mr Soro remain in control of Bouake and Korhogo.
Elections in Ivory Coast are planned for October 2005.