The United States expressed concern Wednesday about reported election campaign problems in Rwanda, where preparations are underway for the Central African country's first presidential polling since the ethnic violence and genocide there in 1994.

The State Department is calling the August 25 presidential vote in Rwanda "an important milestone" in the political transition that began after the 1994 genocide, and says the United States is pleased that four candidates are contesting the election amid strong public interest.

However, in a statement volunteered to reporters, State Department spokesman Richard Boucher said the United States is concerned about recent reports of campaign intimidation, harassment and the use of ethnicity as a means of inciting political division.

Mr. Boucher said the United States "looks forward" to seeing the Rwandan government, political parties, and civil society work cooperatively to ensure that the campaign is conducted in a transparent atmosphere, and that the presidential election is free and fair.

The comments follow angry exchanges between Rwanda's two leading presidential contenders in a country still traumatized by the 1994 violence, in which ethnic Hutu militiamen killed hundreds of thousands of minority Tutsis and Hutu moderates.

Earlier this week, the main opposition candidate, Faustin Twagiramungu, accused incumbent President Paul Kagame and his Tutsi-dominated Rwandan Patriotic Front Party of acts of sabotage and harassment of his supporters.

Mr. Kagame, for his part, accused his chief opponent, a Hutu, of trying to mobilize majority Hutus to vote on ethnic grounds, and suggested he might return the country to ethnic bloodshed.

In his comments here, spokesman Boucher did not address specific complaints but said the United States wants to see a democratic process continue and political openness in Rwanda maintained, as the country heads for the presidential vote and legislative elections in September.

In May of this year, Rwandan voters turned out in large numbers to overwhelmingly approve a new constitution, designed to curb ethnic extremism and pave the way for the two-stage elections, the country's first since 1988.