"It is a matter of grave international concern that these killings took place," British Foreign Secretary Jack Straw told BBC radio on Wednesday.
Aid agencies, diplomats and the media should have "full and immediate" access to the city of Andijan, where the violence occurred, he said.
Several countries have already condemned events in the eastern Uzbek city, where clashes between soldiers and protesters last Friday killed at least 745 people, according to independent witnesses.
The government of autocratic Uzbek President Islam Karimov has put the death toll at 169.
Numerous witnesses have said soldiers who were called to disperse an anti-government demonstration fired indiscriminately into the crowd.
"The government has one version, the opposition has another. It is of crucial importance for the stability of society in Uzbekistan, as well as for the credibility of the government of Uzbekistan, that we get to the bottom of what happened," Straw said.
"Our judgment is that that has to be by an international and independent inquiry."
"The government has one version, the opposition has another. It is of crucial importance for the stability of society in Uzbekistan, as well as for the credibility of the government of Uzbekistan, that we get to the bottom of what happened"
British Foreign Secretary
Earlier on Wednesday, EU External Relations Commissioner Benita Ferrero-Waldner also called for an independent investigation.
"Only then, can the European reaction be objective and the right one," she said in Brussels, reiterating the European Union's deep concern about the violence.
UN High Commissioner for Human Rights Louise Arbour was additionally "deeply concerned over the recent violence and loss of life in Andijan", her office said in a statement.
"The high commissioner also urges the conduct of an independent investigation into the causes and circumstances of the incidents in eastern Uzbekistan," it added.
Straw, who was speaking from Washington where he met US Secretary of State Condoleezza Rice on Tuesday, also condemned the "inadequacy" of a visit organised by the Uzbek authorities for diplomats and journalists to Andijan.
Craig Murray: Western attitude
to Uzbekistan is hypocritical
In a three-hour, state-organised trip on Wednesday, around 36 diplomats, including the ambassadors of the United States, Britain and France, were flown into the city.
"Can we not see some people?" British ambassador David Moran asked Uzbekistan's Deputy Foreign Minister Ilkhom Nematov as the group was deposited back at Andijan airport.
Straw reiterated the concerns. "The ambassadors did indeed try speak to people, but there weren't many people to speak to," he said.
"David Moran, our ambassador, said that he and his colleagues had been very surprised that the visit suddenly, unexpectedly, ended at 12:30 when there was an extra hour-and-a-half before the plane was due to leave."
The response to the crisis from the United States, which considers Uzbekistan a key ally in its "war on terrorism", has been less critical than that of Britain, although Rice said the country needed reform.
"Condoleezza Rice was at pains to point out that President Bush's call for democracy extended universally and without reference to any other kind of relationship that the US government might have with a particular country that needed to extend democracy," Straw said.
Islam Karimov says his troops
killed 'terrorists' only
In a scathing interview published earlier on Wednesday, Britain's former ambassador to Uzebkistan accused both London and Washington of being "hypocritical" in their dealings with the country.
"We back a dictator in Central Asia to get access to oil and gas, and we remove a dictator in Iraq to get access to oil and gas," Craig Murray told London-based newspaper Metro.
Murray lost his job as ambassador last year after accusing Karimov's government of human-rights abuses.