US Assistant Secretary of State Robert Blake has described the situation in southern Kyrgyzstan as an humanitarian crisis.
After visiting refugee camps in neighbouring Uzbekistan, Mr Blake said: "The United States is very concerned about reports of ongoing violence in southern Kyrgyzstan. We urge the provisional government of Kyrgyzstan to take immediate steps to stop the violence."
Kyrgyzstan's interim leader travelled to the south on Friday, pledging to rebuild the region to allow refugees from ethnic bloodletting to return to their homes from squalid camps.
The government has struggled to restore order following clashes between Uzbeks and Kyrgyz around the ancient Silk Road city of Osh that killed about 200 people last week - the worst violence in Kyrgyzstan in two decades.
Hundreds of thousands of refugees, mainly women and children, are crammed into huts and makeshift camps in the sun-scorched plains of the Ferghana valley, many running out of food and water.
Some 400,000 people out of Kyrgyzstan's population of only 5.3 million have fled since June 10, some to refugee camps in neighbouring Uzbekistan.