Secretary-General Kofi Annan has warned the United States, Britain and Iraq that an assault on Falluja risked further alienating the Iraqi people and undermining planned January elections. The warning, contained in letters dated last Sunday and obtained by Reuters on Friday, surfaced as U.S. troops urged civilians to flee the rebel-held city and launched air strikes in preparation for an assault aimed at crippling the insurgency before the elections. Iraqis will vote on Jan. 27, Iraqi Vice President Ibrahim al-Jaafari told Reuters in Baghdad on Friday. A U.N. spokesman said the letters to U.S. President George W. Bush, British Prime Minister Tony Blair and Iraqi Prime Minister Iyad Allawi were "private communications between the secretary-general and heads of state" and declined comment. But U.N. officials made no secret of their fear that a large-scale attack on Falluja could provoke an election boycott by Sunni Muslims and undermine efforts to promote stability. --More 2140 Local Time 1840 GMT