Several members of the Erk Democratic Party and at least one member of the Birlik movement have been arrested or threatened with arrest during the last week. Another opponent of the government, Husniddin Nazarov, has disappeared and -- according to one Uzbek opposition website -- is also under arrest.
Neither Erk nor Birlik is officially registered with Uzbek authorities, though both groups hope to compete in parliamentary elections this December. The recent arrests represent a serious setback to their registration efforts.
Gulomjon Kholmatov, from Uzbekistan's eastern Namangan region, was one of the Erk leaders to be arrested. He is facing charges of illegal opium cultivation. Kholmatov spoke to RFE/RL's Uzbek Service shortly before he was charged and detained. He said the charges against him are false.
"[The authorities] didn't find anything to prove I broke the law. They still haven't said they'll let me go or charged me under Article 270, illegal possession of narcotics. There is an order now from the Prosecutor-General's Office to detain me."
Atanazar Aripov, another Erk leader, says two other party members have been warned during the past several days that they, too, could face charges -- this time for their activities with Erk.
One of the members is based in the southeastern Surhandarya Province; the other is in Bukhara Province.
A member of the Birlik movement, meanwhile, has also been detained. Mukhammadali Korabaev was arrested in Namangan on assault charges. A lawyer for Birlik, Ruhiddin Komilov, says the charges stem from a scuffle involving Korabaev in January, and claims the fight was a provocation.
Uzbek human-rights activist Sobitkhon Ustabaev said Korabaev's arrest is part of a wider campaign by the Uzbek government to weed out political opponents. "The detention of Korabaev is a continuation of the policy, conducted by the government, of frightening the opposition and democratic-thinking people," he said.
Birlik lawyer Komilov says Korabaev is not the only member of the movement to face trial. A similar process is under way in the Jizzak Province aimed against Birlik member Muhiddin Kurbanov.
Still another government opponent -- not associated with either Erk or Birlik -- has gone missing and, according to at least one source, is also under arrest.
Husniddin Nazarov is the son of Obidkhon Nazarov, once the imam of Tashkent's Tokhtaboi Mosque. Obidkhon Nazarov disappeared several years ago, after disputes with authorities in an attempt to keep his home from being demolished during urban renewal projects in Tashkent. His whereabouts remain unknown.
According to his wife, Husniddin Nazarov left his house on 16 May to go to mosque and visit a friend, but did not return home. His mother checked with security officials, a common practice in Uzbekistan where authorities do not always inform family members about detentions. But no information about Husniddin was available.
But "Musulman Uzbekistan," an Uzbek opposition website, yesterday alleged that Husniddin had been arrested near his home by officers of the State Security Service and taken to an unknown location.
The Nazarov family had come under government scrutiny last month, when militia visited the family home and questioned neighbors about the Nazarovs' activities.
Husniddin Nazarov had recently spoken to Western journalists about the recent outbreak of violence and suicide attacks in Tashkent and Bukhara. He accused authorities of using the attacks as a pretext for cracking down on government opponents.
(Oktam Karimov and Shukrat Babajonov of RFE/RL's Uzbek Service contributed to this report.)