At a news conference, Foreign Minister Sadyk Safayev said the attacks were "committed by the hands of international terror, including Hizb ut-Tahrir and Wahhabis."
Uzbekistan outlaws both Hizb ut-Tahrir, which aims to set up a pan-Islamic state that would include post-Soviet Central Asia, and the austere Wahhabi school of Sunni Islam.
President Islam Karimov told the nation in a television address Monday that the perpetrators had been preparing for the "terrorist acts" for at least six months.
"Once again, it should be noted that to carry out such terrorist acts one needs immense sums of money and it is understandable that in the world there are forces that sponsor terrorism," said Karimov.
In London, where Hizb-ut-Tahrir operates openly, the group denied responsibility. If authorities confirm the link to Hizb-ut-Tahrir, it would mark the first time the group has been implicated directly in a terrorist attack. The group says it is nonviolent, but Uzbek authorities have insisted it is a breeding ground for terrorists.
"Hizb-ut-Tahrir does not engage in terrorism, violence or armed struggle," said spokesman Imran Waheed. "We feel these explosions come at a very opportune moment for the Uzbek regime. ... One has to wonder whether the finger of blame should be pointed at the Uzbek regime itself."
The first blast killed ten people late Sunday at an apartment block in Bukhara, 375 miles southwest of Tashkent, when a "terrorist" was preparing an explosive device, Uzbekistan Prosecutor-General Rashid Kadyrov said. Shootouts with "suspected terrorists" left three policemen dead, the prosecutor added.
On Monday, female suicide bombers set off explosions at the biggest bazaar in Tashkent and at a nearby bus stop, Kadyrov said. He added that three policemen, one child and the two suicide bombers died in the Tashkent attacks.
President Karimov said several arrests had been made, but he gave no details. Kadyrov said one suspect in the attacks had been arrested and that authorities were searching for others. He declined to say how many people might have been involved.
Uzbekistan is a close Washington ally in the war on terror in neighboring Afghanistan. It provided a key airbase for U.S. troops following the Sept. 11, 2001, attacks on the United States.
Human rights advocates have sharply criticized Karimov, who ruled Uzbekistan as party leader before the 1991 Soviet collapse and since then as president, for repressing political and religious freedoms.
The last attack of this magnitude in Uzbekistan came in an assassination attempt against Karimov 1999. After that attempt, the government began to crack down on religious extremists. About 7,000 young men deemed political threats were arrested between 1999 and 2001, human rights groups say. The State Department's 2002 human rights report on Uzbekistan estimated the number of political prisoners at 6,500.