A Kenyan police official says one person has died and another was injured in hotly contested primary elections in the capital Nairobi.

Both opposition and ruling party primaries which started last week have experienced chaotic scenes and accusations of rigging. The ruling Jubilee Party had to postpone the start of its primaries because of a shortage of voting materials.

Nairobi police boss Japheth Koome said Wednesday a fight started between rival camps after accusations that a candidate's posters were defaced in the Pangani area. Koome said one person was stabbed and when he fled he was hit by a car and died.

The U.S. government has asked its citizens in or traveling to Kenya to be alert to the security situation as the country heads toward general elections in August.