* Pressure mounts on Kazakhstan to hold transparent investigation
* Kazakh prosecutor-general says U.N. experts welcome
* Authorities hamper investigation attempts by opposition
* Amateur video surfaces; HRW reports ill-treatment in detention
By Dmitry Solovyov
ALMATY, Dec 22 (Reuters) - Kazakhstan has invited United Nations experts to take part in investigating deadly clashes in a western oil-producing region where at least 16 people were killed in the Central Asian nation's worst outburst of violence in decades.
The United States, the European Union and the Organisation for Security and Cooperation in Europe have expressed concerns about the violence and urged Kazakhstan to carry out a transparent investigation into the riots.
Official data show 15 people died in the Dec. 16 clashes between riot police and protesters in Zhanaozen, the town where sacked oil workers had been holding protests for months. Another person died in clashes in a nearby village the next day.
The riots broke out on the 20th anniversary of Kazakhstan's independence from the Soviet Union and have become the most serious challenge faced by President Nursultan Nazarbayev in his two-decade rule of the oil-rich state.
The authorities say police were forced to open fire after being attacked by "criminal elements" and "hooligans" who were threatening civilians. A 20-day curfew is in force in Zhanaozen until Jan. 5.
Prosecutor-General Askhat Daulbayev met Armen Harutyunyan, Central Asia regional representative of the U.N. High Commissioner for Human Rights, on Wednesday, Daulbayev's office said in a statement.
The prosecutor's office said Daulbayev had "specifically stressed the openness and transparency of the activities of the prosecutor-general's office and invited U.N. experts to take part in the investigation of what had happened".
Kazakhstan's opposition has set up a commission of its own to independently investigate the events in western Kazakhstan. The group of more than 20 people includes writers, activists of non-governmental organsisations, and public figures.
Six commission members tried to reach Zhanaozen on Wednesday after obtaining verbal permission from a deputy regional head.
They were stopped by police halfway to the town and were forced to return to the regional capital Aktau, Vladimir Kozlov, leader of the unregistered Alga! opposition party, told Reuters. He was in the group that failed to reach Zhanaozen.
"I believe that, even if the authorities give access to international experts, it will concern only the evidence that raises no questions," Kozlov said.
TORTURE ALLEGATIONS
An amateur video, apparently taken on a mobile phone from an apartment window, was posted on the Internet on Tuesday showing police shooting at fleeing protesters. The clip's authenticity could not be verified independently.
Radio Liberty reported that Erlan Idrisov, Kazakhstan's ambassador to the United States, told a news conference in Washington on Wednesday that the Kazakh government was aware of the coverage and planned to investigate it.
New York-based Human Rights Watch on Thursday urged the authorities to investigate immediately allegations of torture and ill-treatment of detainees following violence in Zhanaozen and to hold those responsible accountable.
It said that the state of emergency restrictions, limiting access to Zhanaozen, heightened concerns of mistreatment. The rights watchdog said it had received information that people in detention had been beaten.
"Allegations of torture in Zhanaozen are profoundly disturbing and the Kazakh government should immediately conduct an impartial investigation," said Rachel Denber, deputy Europe and Central Asia director at Human Rights Watch.
"There is never any justification for torture or ill-treatment." (Reporting by Dmitry Solovyov Editing by Maria Golovnina)
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