Kyrgyzstan has begged Russia for military help to quell ethnic rioting as the country's second largest city burned and thousands of minority Uzbeks fled to the border.

Kyrgyzstan made the appeal after at least 63 were killed in the worst violence since the former president was toppled in April.

The interim government in Kyrgyzstan, which hosts US and Russian military bases, said it was powerless to stop armed gangs from burning down the homes and businesses of ethnic Uzbeks in parts of Osh.

The unrest is the worst violence since former President Kurmanbek Bakiyev was toppled in a bloody uprising in April and fled the country.

It comes as a crucial test of the interim government's ability to control the country, hold a June 27 vote on a new constitution and go ahead with new parliamentary elections scheduled for October.