Troops have been brought to the town, he said. The assault is expected after dusk.
The rally which began this morning continues on the central square of Karasuv in front of the local administration building.
Leaders of the rally say that the situation is under their control, heads of the public order maintenance squads have been appointed and there will be no unrest in the city.
According to witnesses, rally participants have captured the head of the Kurgantepa district of the Andizhan region. He tried to reach agreement with them in the morning.
Earlier, witnesses told RIA Novosti that the buildings of the police branch office, district administration and tax inspection were on fire in Karasuv.
On Saturday morning people gathered on both sides of the Kyrgyz-Uzbek border and repaired the bridge across the border river. Earlier, the bridge across the small mountain river connected the two republics but was taken apart. About half of the population of the Osh district are ethnic Uzbeks.
People crossed the bridge from Kyrgyzstan to Uzbekistan and gathered for a rally, the witness said.
Kurasuv, a town on the border with Kyrgyzstan, is several dozen kilometers away from Andizhan.
After the collapse of the USSR, the town of Kara-Su was divided into two parts - Kara-Suu (Kyrgyzstan) and Ilyichevsk (now Karasuv, Uzbekistan). The two parts are divided by the border river. No border guard posts are present.
