Supporters of Kurmanbek Bakiyev, Kyrgyzstan's ousted leader, have taken over the local government headquarters in the southern city of Osh.
The protesters scuffled with guards and entered the government building on Thursday after holding a demonstration that drew about 1,000 people.
The Kyrgyz government responded by saying it would take unspecified measures to restore authority in the area.
Bakiyev fled Kyrgyzstan last month after an interim government seized power following street unrest that claimed 85 lives in the capital, Bishkek, and elsewhere.
The interim government has since struggled to stamp its authority across the country, particularly in Bakiyev's southern power base.
On Wednesday, the interim government faced its first large public protest in the capital as hundreds of opponents - many members of Bakiyev's Ak Zhol party and the allied Communists - demonstrated against the dissolution of parliament.
The United States and Russia have both expressed support for the interim government, which has promised to hold new parliamentary elections in October.
Both countries have air bases in Kyrgyzstan. The US base at Manas airport is key to American efforts to supply forces fighting in nearby Afghanistan.
PHOTO CAPTION
Ousted Kyrgyzstan President Kurmanbek Bakiyev makes a statement in Minsk April 21, 2010.
Al-Jazeera