The New York-based group released the most comprehensive report so far into the bloodshed in the town of Andizhan but said key questions -- including the true death toll which witnesses have said could be over 500 -- were still unanswered.

"The scale of the killings and the deliberateness of the security officials means this can only be described as a massacre," Kenneth Roth, executive director of Human Rights Watch, said as he presented the report.

The report said the wounded were left untreated for hours and some were finished off by troops where they lay. Many bodies were still unaccounted for, it said.

Witnesses to the May 13 killings say Uzbek troops opened fire without warning on a crowd of unarmed demonstrators, among them women and children, who were protesting about poverty and government repression.

"An independent, international inquiry is required to get at the truth of what happened," Roth told reporters.

"The Uzbek government and parliament say we should trust them to investigate ... but in fact the government is blocking access to information," Roth said.

Uzbek President Islam Karimov has said the death toll was 173 people and that most of the victims were armed terrorists who were trying to overthrow the government and install Islamic rule in the ex-Soviet state.

Karimov has rejected calls from the United Nations, the European Union and the United States for an international inquiry. The Uzbek parliament is conducting its own inquiry.

Uzbekistan, with 26 million people Central Asia's most populous state, is an ally in the U.S.-led "war on terror," leasing a base to the U.S. military to support its operations in neighboring Afghanistan.

But Washington should now scrap plans to expand the base to exert pressure on Karimov, Human Rights Watch said.

"I hope the Bush administration realizes that Karimov is no longer an ally. He has turned into a deep liability," Roth told a news briefing.

"BOWLING ALLEY"

A senior official in the Uzbek capital, Tashkent, told Reuters an official government response to the Human Rights Watch report was not ready.

The report was presented in Moscow because Roth was attending the group's board meeting in the city.

A Reuters reporter in Andizhan on May 13 witnessed some of the killing, while a second Reuters reporter afterwards collected witness accounts in the town and saw evidence suggesting the authorities were secretly burying victims.

The rights group's report -- based on 50 interviews with witnesses -- said troops fired directly into a crowd of protesters in Andizhan's main square without issuing any warning, although in two cases they fired into the air.

No one in that crowd was armed, it said, contradicting the Uzbek government's version. A handful of protesters with weapons were standing apart from the main body of people, it added.

And it ruled out the involvement of Islamic militants in inciting the violence. Before the shooting, protesters "were shouting 'Ozodliq!' ('Freedom'), not 'Allahu Akbar! ('God is Great')," the report said.

It backed up earlier accounts of troops trapping fleeing protesters outside the town's School No. 15, then opening fire.

"It was like a bowling game, when the balls strike the pins and everything falls down ... There were bodies everywhere," the report quoted one unnamed witness as saying.

In Geneva, the International Committee of the Red Cross (ICRC) pressed Uzbek authorities to allow it to visit people wounded or detained in Andizhan.

"Restoring family links is a priority as many Uzbeks still do not know whether missing next-of-kin are dead, injured or arrested or whether they fled the violence to another part of the country," it added.

(Additional reporting by Shamil Baigin in Tashkent and Stephanie Nebehay in Geneva)