ALMATY, Kazakhstan — Kazakhstan shouldn't use an official investigation into recent violence to crack down on opposition politicians and government critics, international rights groups said Wednesday.

New York-based Human Rights Watch said this week's arrest of activists and journalists suggests authorities want to silence their detractors. Washington-based Freedom House said the arrests "undermined respect for fundamental freedoms."

Among those detained and facing charges of inciting the unrest are unregistered Alga party leader Vladimir Kozlov and newspaper editor Igor Vinyavsky.

Security services say they are investigating what led to fatal clashes in December between police and striking oil workers in the western oil town of Zhanaozen.

At least 16 people were killed in Zhanaozen during the clashes on Dec. 16, a rare outbreak of unrest in the generally orderly country.

While the opposition argues that the government failed to take heed over protesters' calls for higher salaries, authorities say violence was instigated by external forces seeking to sow instability.

"The Kazakhstan authorities' actions will taint the investigation. A genuinely pluralistic and rights-abiding government tolerates dissent, does not quash it," Hugh Williamson, HRW's Europe and Central Asia director, said in a statement.

The National Security Committee, the successor agency to the Soviet-era KGB, earlier this month detained regional Alga party official Aizhangul Amirova, who has also been charged with inciting unrest, an offense punishable by up to 10 years in prison.

On Monday, police swooped on the Alga headquarters in Almaty, Kazakhstan's commercial capital, and searched the homes of several party officials. Security service officers seized computers, flash memory sticks and documents from the office and homes.

Other government opponents unaffiliated to Alga, such as Rukh Pen Til youth opposition group leader Zhanbolat Mamai, were questioned and ordered not to leave Almaty.

Vinyavsky, who edits independent weekly newspaper Vzglyad, has been charged with using his publication to call for "the overthrow of the constitutional order."

"If the Kazakh authorities can prove these political activists were involved in the violence in Zhanaozen, they shouldn't need to resort to using vague and undefined criminal allegations to imprison them," Williamson said.

Kazakhstan, a vast sparsely populated nation of  16 million, is becoming increasingly important as a major supplier of oil and gas, and the country also is key to the northern delivery route for supplies to the U.S.-led military operation in Afghanistan.

It has strenuously attempted to project itself as a rapidly modernizing country but has come under fire for its lack of political reforms.

"Kazakhstan, as a former chair of the Organization for Security and Cooperation in Europe, must live up to its promise to the international community that it will advance democracy and human rights," said Susan Corke, director for Eurasia programs at Freedom House.

The Zhanaozen clashes erupted after a months-long sit-in by oil workers discontented with salaries. Although the demonstrating laborers were fired by their employers over the summer, the protests continued.

After months of calm demonstrations, the situation quickly deteriorated in mid-December when, according to the government account, protesters attacked participants in a children's concert in the main square.

Authorities initially argued that police fired on protesters in self-defense, but they were forced to revise their account when amateur footage appeared online showing police shooting at retreating rioters.