The UN said a unit of its contingent in Bouake, a northern rebel stronghold, had been confined to base.
It would not give the nationalities of those troops under investigation.
Claims of sexual abuse have been made against UN troops on various missions, prompting ex-UN chief Kofi Annan to declare a "zero tolerance" policy.
"There have been crimes such as rape, paedophilia and human trafficking," he said in December 2006, shortly before leaving office.
He said sexual exploitation and abuse were "utterly immoral" and at odds with the UN mission, and would be punished.
Last Mod: 21 Temmuz 2007, 08:09
A UN statement said the latest allegations had been uncovered by an internal inquiry, and a full investigation was now under way.
"But due to the serious nature of the allegations, the United Nations has taken the decision to suspend all activities of the contingent and has cantoned the unit within its base," it said.
The exact nature of the alleged offences has not been officially disclosed, but they are believed to involve sex with underage girls.
About 9,000 troops serve under the UN in Ivory Coast, which has been split between areas controlled by government and rebel forces.
The UN Security Council this week voted to extend the mission until January, in the hope that it can help create the conditions for elections, that have repeatedly been delayed.
According to the UN website, troops in Bouake come from Morocco, Pakistan, Bangladesh and Ghana.
It is not known which country's troops are under suspicion but, in an unusual move, the UN has confined its entire force in the town to barracks.
It is a sign of how seriously the UN is taking these latest accusations, says the BBC's Peter Miles.