The coordinated bombings -- which took place outside the U.S. and Israeli embassies and inside the Uzbek prosecutor general's office -- killed three law enforcement officers and a security guard in addition to the three bombers.
Islamist websites have carried competing claims of responsibility for the attacks from organizations like the Islamic Movement of Uzbekistan (IMU) and a previously little-known group called Islamic Jihad in Uzbekistan.
Nevertheless, President Islam Karimov has suggested that another Islamist movement, Hizb ut-Tahrir, is responsible for the attacks: "There are some groups -- associations, organizations that call themselves human-rights organizations -- which are trying to say that Hizb ut-Tahrir is an innocent lamb, harmless. Actually, this group deceives many and is recruiting new members. I emphasize again their spiteful intentions will be visible when [there are more attacks]. But, unfortunately, by then it will be too late."
Karimov suggested Hizb ut-Tahrir is also responsible for a wave of violence this spring (late March-early April) in Tashkent and the ancient Silk Route city of Bukhara. Forty-seven people were killed in the violence, including 33 attackers.
Oleg Bichenov, chief of Tashkent's antiterrorism police, told the Associated Press that the bombings were in retaliation for the ongoing trial of suspects charged in the spring attacks.
Two of those defendants have confessed to being forced to join an extremist group called Jamoat, or "Society." One of the defendants added that Jamoat's leader had cooperated with Hizb ut-Tahrir.
But Imran Wahid, the head of Hizb ut-Tahrir's London office, denies the group was involved in the latest attacks or the ones earlier this year. He says the group does not engage in terrorism, violence or armed struggle: "Karimov's regime is a weak regime. Hizb ut-Tahrir continues to gain in popularity in Uzbekistan and Central Asia, and therefore Karimov is desperate to malign the image of Hizb ut-Tahrir within Uzbekistan and Central Asia."
The group, which is believed to have up to 20,000 members in Central Asia, is not known to have been involved in any violent action in the region.
But Uzbek intelligence officers have warned that Hizb ut-Tahrir -- which favors the creation of an Islamic caliphate throughout Central Asia -- could easily turn violent.
Paul Bergne, a former British ambassador to Uzbekistan, told RFE/RL he doubts Hizb ut-Tahrir was involved in either of the two attacks this year: "So far I haven't seen any persuasive evidence that [Hizb ut-Tahrir] has changed its policy [of nonviolence]. So -- at first sight, at least -- it seems unlikely that Hizb ut-Tahrir was behind the bomb explosions."
Bergne says he believes the group responsible for the bombings is most likely a part of the IMU -- possibly the Islamic Jihad in Uzbekistan, which had already claimed responsibility for the earlier attacks in Tashkent and Bukhara.
The IMU was blamed for a series of bombings in 1999 in Tashkent. It has now been two years since the group was believed to have been largely destroyed by the U.S.-led military campaign that toppled Afghanistan's Taliban regime.
(Khurmat Babadjanov of RFE/RL's Uzbek Service contributed to this report.)