* Row over gold venture with Canada company sparks unrest
* Protest leader calls for toppling of Kyrgyz government
* Such rallies triggered two violent coups since 2005
* Stand-off with nationalists may deepen north-south divide
* Centerra shares fall about 1 pct to C$12.28 in Toronto
By Olga Dzyubenko
BISHKEK, Oct 3 (Reuters) - Kyrgyz police fired tear gas on Wednesday to stop protesters storming government headquarters in what their leader called a coup bid after the new premier rejected demands to nationalise a gold-mining venture with a Canadian company.
The volatile Central Asian state has seen several attacks on the government since Kyrgyzstan's independence from the Soviet Union in 1991. The bloodiest protests, in March 2005 and April 2010, toppled two presidents, who then fled abroad.
Wednesday's rally, with its direct call to overthrow the government, was the most violent in the capital Bishkek since the April 2010 revolt that ousted President Kurmanbek Bakiyev.
The clashes erupted two days after new Prime Minister Zhantoro Satybaldiyev travelled to the Kumtor gold mine operated by Canada's Centerra Gold Inc and gave assurances the venture would not be nationalised.
His pledges to defend foreign investment vital to Kyrgyzstan's economy angered local nationalists, who failed to muster enough support in parliament in June to pass a law that would have placed the Kumtor mine under state ownership.
Police used tear gas and stun grenades to clear some 2,000 demonstrators from Bishkek's central Ala Too square after about 200 people climbed a fence surrounding the building housing the government and parliament.
"We must occupy the offices of ministers and members of parliament and spend nights there ... in order to create a new state system which will truly serve the people," Kamchibek Tashiyev, leader of the parliamentary faction of the nationalist Ata Zhurt party, told supporters from the back of a truck.
Brief scuffles broke out, with Tashiyev's mainly young supporters pelting police with stones.
"I will assume all responsibility, follow me!" Tashiyev shouted through a megaphone.
"Bureaucrats in the government promised that they would take Kumtor back and it would work for the good of the people ... Kumtor belongs to our nation, and we must change the entire state system and replace this government."
Police managed to repel protesters into side streets while several hundred others - some on horseback - took up guard along the perimeter of the white-marble government building popularly known as "The White House".
Kyrgyzstan's GKNB security service, police and prosecutors will jointly investigate Wednesday's clashes and decide whether some protesters should be charged, a police spokesman said. Tashiyev's whereabouts after the clash were unknown.
NATIONALISM WIDENS REGIONAL SCHISM
Satybaldiyev, a 56-year-old technocrat, was elected by an overwhelming vote in parliament on Sept. 5 on pledges to fight corruption and restore economic growth in the mountainous, mainly Muslim nation of 5.5 million people.
Kyrgyzstan, which hosts both U.S. and Russian military air bases, lies on a drug trafficking route out of Afghanistan.
Kumtor Operating Co - the largest gold mine operated in Central Asia by a Western-based concern - is vital for the shaky Kyrgyz economy. It accounted for 12 percent of gross domestic product and more than half of all Kyrgyz exports in 2011.
Earlier official attempts to attract large-scale investment to the impoverished but resource-rich country snagged on protests by nationalists angered by what they describe as a sell-off of Kyrgyzstan to foreigners.
Centerra, which has operated in Kyrgyzstan since the 1990s, reached a revised ownership agreement with the government in 2009. The state holds a 33 percent stake in the company, and also receives a 14 percent tax on gross revenue from its Kumtor mine, a Centerra spokesman said.
Gold output at Kumtor has sagged this year, as ice movement in the high-altitude pit slowed operations, leading the company to trim its production forecast by a third earlier this year.
On Aug. 28, the Kyrgyz government had to cancel its first televised auction aiming to sell new mining licences after nationalist protesters stormed a TV studio.
Analysts say nationalist attempts to use Kumtor to remove the government may not only scare off potential investors but also deepen the divide between Kyrgyzstan's more developed north and ethnically divided south.
In June 2010, around 500 people died in ethnic clashes between Uzbeks and the Kyrgyz, whose epicentre was in the city of Osh, the unofficial capital of Kyrgyzstan's south.
Bishkek's grip is tenuous in the poorer, nationalist south where Tashiyev's Ata Zhurt party and allies have strong support.
"I am afraid that if this nationalist regionalism spreads, there is a risk that Tashiyev will now mobilise more and more of his supporters in the south," said politologist Mars Sariyev.
Shares of Centerra fell 1.13 percent to C$12.28 on Wednesday morning on the Toronto Stock Exchange. The stock is down more than 30 percent this year.