Investigators from the FBI have joined Uzbek police probing suicide attacks on the US embassy in Tashkent and other sites, diplomatic sources say.
The embassy blasts came amid a high-profile terror trial
An Uzbek policemen has died of his injuries - the fourth person to die in addition to the three bombers who also attacked the Israeli embassy.
The third attack on Friday targeted the chief prosecutor's office.
They were the first attacks on foreign missions in the ex-Soviet central Asian state since independence in 1991.
Both the US Federal Bureau of Investigation and Israeli officials are involved in the investigation, anonymous sources at the two countries' embassies said.
The explosions came days after 15 alleged Islamist militants went on trial in Tashkent, accused of involvement in a wave of violence in the spring in which at least 47 were killed.
That trial was suspended on Monday, "due to the illness of a defence lawyer", a spokesman at the Uzbek Supreme Court said.
Police chief Oleg Bichenov told the Associated Press news agency that Friday's attacks were connected to the terror trial.
"These are links in one chain," he said.
The police sergeant who died in hospital overnight had been on duty at the US embassy. Another guard at the embassy was also killed along with two at the Israeli embassy, while seven people were lightly injured.
Uzbek officials said earlier that a number of people had been arrested after the attacks but gave no details.
Interior Minister Zakirdzhon Almatov told Russia's Itar-Tass news agency they had identified one of the three suicide bombers.
Islamist websites have carried competing claims of responsibility for the attacks.
One, the little-known Islamic Jihad Group in Uzbekistan, said they were a protest against injustice and to show support for Palestinian, Iraq and Afghan fighters.
President Islam Karimov cut short his holiday in the Crimean region of Ukraine to return home.
Uzbekistan has been a staunch ally of the US in its war on terror but the Uzbek authorities are widely accused of human rights abuses.