The Central Asian state of Kazakhstan has moved to ban two opposition movements critical of President Nursultan Nazarbayev and to close dozens of opposition media outlets for "propagating extremism".

In a step the opposition denounced as an attack on dissent in the oil-exporting former Soviet republic, prosecutors linked their request to last month's jailing of Vladimir Kozlov, leader of the unregistered Alga! or "Forward!" party.

Kozlov was sentenced to seven-and-a-half years for trying to rally workers in a failed attempt to topple the government. After his trial, the United States accused Kazakhstan of using its justice system "to silence opposition voices".

Nazarbayev, 72, has run Central Asia's most successful economy and largest oil producer for more than two decades, but has tolerated little dissent as he has pursued market reforms and attracted more than $150 billion in foreign investment.

As well as leading Alga!, Kozlov, a fierce critic of Nazarbayev, was leader of the country's unofficial Halyk Maidany, or People's Front movement, which tried to unite groups with specific grievances against the government.

He was found guilty of colluding with fugitive anti-government billionaire Mukhtar Ablyazov and of orchestrating dissent among striking oilmen in the prelude to riots last December that killed 15 people and dented Kazakhstan's reputation for stability.

Nurdaulet Suindikov, a spokesman for the prosecutor-general's office, on Wednesday accused the two opposition movements Kozlov led and various media outlets of "propagating extremism".

"Kozlov's sentence established that the activity of the unregistered Alga! and Halyk Maidany movements, as well as the activity of a number of mass media outlets, was extremist," he said.

Suindikov said prosecutors in Kazakhstan's commercial capital, Almaty, had asked a court to ban the two movements as well as the media outlets.

KAZAKHSTAN'S BIN LADEN?

Suindikov said prosecutors were seeking the closure of eight newspapers and 23 Internet sites that operated under the umbrella of the Respublika publisher, as well as the Vzglyad newspaper and its Internet sites.

Kazakhstan's marginalised opposition enjoys little support among voters. The country has never held an election that Western monitors have deemed fair, but Nazarbayev is popular in the country of 17 million for presiding over relative stability.

Oksana Makushina, deputy editor-in-chief of the Golos Respubliki newspaper - part of the Respublika group - said her publication would try to get round any court order.

"They may close the paper in legal form, but given the presence of the Internet, it is hard to do so in reality," she told Reuters. "We will continue fighting, unless we are put in a prison cell next to Kozlov."

Mikhail Sizov, another leader of the Alga! party, said he believed Kozlov's imprisonment for his part in the Zhanaozen riots was the beginning of a wider campaign to destroy the entire opposition movement in Kazakhstan.

"There is virtually an undeclared war going on between Mukhtar Ablyazov and Nursultan Nazarbayev," Sizov told Reuters.

The satellite TV channel K+ and the Internet portals run by Stan TV are among the media outlets targeted by prosecutors. State TV ran a documentary this week that identified Ablyazov as the financial backer of both channels.

Baurzhan Musirov, director of Almaty-based Stan Productions, which runs the Stan.KZ portal, denied it was financed by Ablyazov.

Ablyazov has been on the run since February, when he was sentenced to 22 months in prison for contempt of court in Britain, where he had earlier received political asylum. His whereabouts are unknown.

A theoretical physics graduate who built a fortune by snapping up banking and media assets in the 1990s after the Soviet Union collapsed, Ablyazov has said he fell out with Nazarbayev after campaigning for a change of government.

He has failed to appear in a vast fraud case being heard in Britain, where his former bank, state-owned BTA, has brought nine charges against Ablyazov and his allies. In the same case, BTA has frozen assets worth around $6 billion.

Kazakh political analyst Aidos Sarym said he believed the current campaign against the opposition was aimed at presenting Ablyazov as a "home-grown Bin Laden" or Kazakh version of the late al Qaeda leader.