"Within the last two days, police have detained dozens of our party members, saying we are hiding terrorists involved in the recent uprising in the Fergana Valley," Vasilya Inoyatova, the leader of the outlawed Birlik party, or Unity, said by phone from a police station in the capital, Tashkent.
A human rights activist, Surat Ikramov, said Monday that police were preventing him from leaving his home in Tashkent and that he had received calls from numerous other rights activists who either had been detained or were forcibly isolated in their homes.
The detentions follow the uprising that erupted in the eastern city of Andijan on May 13, when militants seized a local prison and government headquarters and thousands of protesters hit the streets.
Uzbek authorities say 173 people died, but deny they opened fire on unarmed civilians.
Rights advocates say up to 750 people were killed in the violence.
Inoyatova said at least 20 activists who had come from the eastern Fergana Valley for a party meeting in Tashkent were detained Monday morning, and that other Birlik members and her relatives, including her husband and 26-year-old son, had been arrested earlier.
On Sunday, Inoyatova and representatives of three other outlawed opposition parties met with three US senators -- John McCain of Arizona, Lindsey Graham of South Carolina, and John Sununu of New Hampshire _ who added their voices to Western calls for the Central Asian nation's leadership to allow an international investigation into the bloodshed.
Authoritarian President Islam Karimov has rejected UN and Western calls for an international inquiry, saying Uzbek authorities would conduct their own probe.
He has blamed the unrest on Islamic extremists, accusing them of killing hostages and of using civilians as human shields.
The US legislators said the Uzbek government's harsh response to the unrest had made it difficult to maintain the relations the United States would like to have with its ally in the war on terror.
Uzbekistan hosts hundreds of American troops at an air base near the border with Afghanistan.