A senior U.S. diplomat on Saturday urged Kyrgyzstan to create conditions for the safe return of refugees displaced by recent riots in the south of the country.

U.S. Assistant Secretary of State Robert Blake urged the Kyrgyz interim government to take immediate action to stop the violence and called for an investigation into the unrest.

An estimated 400,000 refugees have taken shelter in camps, which are crowded and have poor sanitation, and are in urgent need of aid.

The diplomat said it was important for the interim government to "establish an atmosphere of trust and security" so that the refugees in Uzbekistan and those in Kyrgyzstan can feel confident that they can safely return to their homes.

The UN Office for the Coordination of Humanitarian Affairs said an estimated 100,000 refugees had fled to neighboring Uzbekistan, and 300,000 others were still seeking aid within Kyrgyzstan.

Ethnic clashes broke out in mid-June in the major southern city of Osh and later spread to the Jalalabad region. The official death toll stood at 191 as of Friday, but interim leader Roza Otunbayeva said during an inspection tour of Osh that the real number was likely to be 10 times higher.