* Left-wing activist group backs striking oil workers
* UzenMunaiGas employees say will prolong five-week strike
* KazMunaiGas EP says strike illegal, output affected
By Anna Andrianova
MOSCOW, June 30 (Reuters) - A group of striking Kazakh oil workers vowed to prolong their five-week dispute over pay and conditions after travelling to Moscow on Thursday in a rare show of dissent against authorities in the Central Asian state.
Three employees of UzenMunaiGas, a unit of London-listed oil producer KazMunaiGas Exploration Production (KMGq.L), said they had travelled to Russia to publicise a dispute they say is being ignored by local media and politicians in Kazakhstan.
The visit was organised by Igor Yasin, who said he was a Russian member of the Committee for a Workers' International, a left-wing activist group.
KazMunaiGas EP, Kazakhstan's second-largest oil producer, said in a statement on Tuesday it had lost 150,000 tonnes (about 3,000 barrels per day) of oil production from the Uzen field in western Kazakhstan since the strike began on May 26.
As a result of the strike and a slight reduction in output at other operating assets, the company has shaved 4 percent from its previous 13.5 million-tonne forecast for consolidated crude oil production this year.
Kazakhstan, the largest economy in Central Asia, holds about 3 percent of the world's recoverable oil reserves and has doubled crude output over the last decade to become the second-biggest producer in the former Soviet Union after Russia.
Labour disputes are relatively rare in the vast nation, which President Nursultan Nazarbayev has ruled since before it gained independence 20 years ago, but the Uzen strike followed closely on the heels of a brief dispute at another Kazakh field.
"We are under pressure from our employer," 33-year-old Marat Zhusipayev, who repairs oil wells at the Uzen field, told a news conference in the Russian capital.
Protesters said their salaries had been cut and their lawyer imprisoned on false charges. They said almost 16,000 people had gone on strike at the height of the protest, which KMG EP says is illegal.
The company said its UzenMunaiGas unit, based in the town of Zhanaozen in Mangistau region, employed about 9,000 people. It said 2,500 people were on strike at the peak of the dispute, but that only 650 people were continuing to protest.
"Their demands are groundless and illegal," said KazMunaiGas EP spokesman Daulet Zhumadil. He said salaries had not been cut.
Zhumadil said around 250 employees had been fired for breaching their contract terms, but that the company was encouraging others to return to work without fear of sanction.
"Hopefully, we will persuade them to return to their workplaces," he said.
Maksat Dosmagambetov, another striking worker, said he and his colleagues had followed procedure but had not received satisfactory responses to their written requests to management and other institutions.
"We will continue to strike," he said. "We do not have any other choice." (Editing by James Jukwey)