The US state department said rights to freedom of expression and association are core tenets of democracy.
During the protests, one person was shot dead in Kisumu, and two were injured in Migori.
Property of an unknown value was destroyed in the chaos that erupted as police tried to stop a march by the opposition in parts of the country.
Police say up to 20 cops were injured and three cars destroyed and that they arrested over 20 suspects over the same.