Unrest spread through eastern Uzbekistan after a crackdown by security forces left up to 500 dead in Andijan, with disturbances reaching three other towns -- including one that reportedly left 200 dead.
The clashes in the region bordering Kyrgyzstan were the worst since Uzbekistan gained independence from the Soviet Union in 1991.
President Islam Karimov's government has denied opening fire on demonstrators as witnesses have claimed, instead blaming Islamic extremists for the violence. The authoritarian government has restricted access for reporters in the affected areas.
But if the reports of more than 700 deaths since Friday hold true, and if Uzbek forces were behind the killing -- as most reports indicate --it would be some of the worst state-inspired bloodshed since the massacre of protesters in China's Tiananmen Square in 1989.
Saidjahon Zaynabitdinov, head of the local Appeal human rights advocacy group, said Monday that government troops had killed about 200 demonstrators on Saturday in Pakhtabad, about 20 miles northeast of Andijan. There was no independent confirmation of his claim.
That violence would have come a day after some 500 people reportedly were killed in Andijan --Uzbekistan's fourth-largest city --when government troops put down a prison uprising by alleged Islamic militants and citizens protesting dire economic conditions.
Andijan remained tense on Monday after gunfire continued throughout the night. Residents said government troops were fighting militants in an outlying district, but the claim could not be confirmed.
Alexei Volosevich, an Andijan correspondent for the Fergana.ru Web site, said witnesses told him that militants fired at police from apartment buildings near the prison and that police eventually killed the assailants. There was no word about police casualties.
Troops and armored personnel carriers formed a tight circle around the city center, where the local administration building --at the center of Friday's violence --was on fire late Sunday.
Men were digging what appeared to be a large common grave at a local cemetery under the watch of Uzbek security service agents.
"The people now are more afraid of government troops than of any so-called militants," Zaynabitdinov told Associated Press Television News.
In a separate clash Sunday in the border town of Teshiktosh, eight soldiers and three civilians were killed and hundreds of Uzbeks fled into neighboring Kyrgyzstan, witnesses said.
In another border community, Korasuv, an estimated 5,000 people went on a rampage on Saturday and forced authorities to restore a bridge across a river that marks the border with Kyrgyzstan.
The violence puts the United States in a difficult position because it relies on Karimov's government for an air base in the country and anti-terrorism support. So far US authorities have only called on both sides to work out their differences peacefully.
(Associated Press reporters Bagila Bukharbayeva and Burt Herman contributed to this report from eastern Uzbekistan).