Fifteen men pleaded guilty Tuesday to participating in an uprising in eastern Uzbek city of Andijan last May. Human Rights Watch has said it doubts the trial will be fair and repeated its call for an independent, international investigation into the events in Andijan.

In a new report, Human Rights Watch accuses the government of Uzbekistan of conducting a crackdown to conceal the truth about what happened in Andijan on May 13.

That day, anger over the trial of more than 20 Muslim business-owners for alleged Islamic extremism spiraled into an outbreak of protests and violence.

Before order was restored a day later, hundreds of civilians were dead - allegedly gunned down by government forces as they tried to flee the scene of an anti-government demonstration.

The government of President Islam Karimov, who has ruled Uzbekistan with an increasingly authoritarian hand, puts the death toll at 187 and blames Islamic extremists for the casualties. President Karimov denies that Uzbek troops used deadly force against civilians.

On Tuesday, 15 men went on trial in Tashkent on charges related to the May 13 protests.

The Moscow deputy director of Human Rights Watch, Alexander Petrov, doubts the trial will be fair. His organization takes issue with the way the government has investigated the incident and its failure to prosecute government forces.

"The problem is that, first of all, the investigations, and detentions, and arrests were conducted with massive violations of procedural rules of international standards," said Alexander Petrov. "And, the second is that the government does its best to avoid investigations [and findings] of guilt of servicemen [local police and troops] who participated in the massacre."

Mr. Petrov says the government can only show good faith now if it allows an international inquiry into what really went on in Andijan.

Amnesty International has made similar appeals. So far, President Karimov has ruled out any international investigation, saying the trials beginning Tuesday will reveal the truth.

Mr. Petrov of Human Rights Watch is skeptical, in large part, he says, because the government has detained several prominent human rights activists who had disputed the official version of events.

"In particular, one prominent human rights activist - his name is Saidjahon Zainabitdinov - was arrested right after the 13th events and put on trial and [the] charges against him are just outrageous," he said.

Mr. Petrov says other actions taken by the government include threatening and harassing international human rights workers and political activists.

President Karimov has accused international rights groups and charities of trying to spark a revolution in Uzbekistan, much like those seen in the former Soviet Republics of Ukraine and Georgia.

More than 100 people face charges in related to the May 13 protests, and Uzbek officials say they could face long jail terms or the death penalty.