By Raushan Nurshayeva

ASTANA (Reuters) - A dispute over Central Asian water resources risks provoking military conflict in the former Soviet region, Uzbek President Islam Karimov said on Friday, in a stinging criticism of plans by neighboring states to dam rivers for hydropower projects.

Uzbekistan, Central Asia's most populous country, depends on the rivers that rise in Kyrgyzstan and Tajikistan to irrigate farmland. It has long been opposed to its neighbors' plans to revive colossal Soviet-era projects to build dams upstream.

"Water resources could become a problem in the future that could escalate tensions not only in our region, but on every continent," Karimov told reporters in the Kazakh capital Astana.

"I won't name specific countries, but all of this could deteriorate to the point where not just serious confrontation, but even wars could be the result."

Uzbekistan has 8.2 people per hectare of irrigated land, one of the highest proportions in the world, LaTUK, a Moscow-based think tank focusing on Central Asia, said in a study published in its publication 'The Great Game'.

With a population of 29 million, forecast to expand beyond 33 million by 2025, Uzbekistan will need more water. The amount it receives have already fallen by nearly 20 percent in the last few years, LaTUK research showed.

"This gradual reduction in water supply is fraught with immense conflict potential, both in relations among the regional states and for social stability inside the country," it wrote.

Upstream, the mountainous republics of Tajikistan and Kyrgyzstan are among the poorest in the former Soviet Union. Almost entirely dependent on imported power, both countries want to use their rivers to generate electricity.

Kyrgyzstan launched its Kambarata-2 power station in 2010 and is pursuing Russian investment for the much larger Kambarata-1 station, an estimated $2.5 billion project due for completion by 2021.

Karimov was particularly scathing of Tajikistan's flagship Rogun dam, a $2.2 billion project frozen pending completion of a World Bank assessment. At 335 meters, Rogun would be the highest man-made dam in the world.

"They're going for the Guinness world record, it would seem, but we're talking here about the lives of millions of people who cannot live without water," Karimov said.

"These projects were devised in the 70s and 80s, when we were all living in the Soviet Union and suffering from megalomania, but times change," said Karimov. "Hydropower structures today should be built on a different basis entirely."

Tajik government officials were not available for comment.

'WE CANNOT REMAIN SILENT'

Water management has been a controversial issue in Central Asia for centuries. The diversion of rivers to cultivate cotton in Soviet times was responsible for the depletion of the Aral Sea, which straddles the border of Uzbekistan and Kazakhstan.

Karimov was visiting Astana to drum up support from Kazakh President Nursultan Nazarbayev, another veteran Central Asian leader who, in 2010, expressed support for the resurrecting of a Soviet scheme to divert Siberia's rivers southward.

"Kazakhs and Uzbeks have lived for many centuries along the lower reaches of the Syr-Darya river," Karimov said, referring to one of the region's biggest rivers. "For that reason, we cannot remain silent."

Nazarbayev was more restrained. "We send brotherly greetings to our neighbors upriver (Kyrgyzstan and Tajikistan), a reminder that we downriver - Kazakhstan, Uzbekistan and Turkmenistan - are feeling the water shortage ... We hope to resolve these issues together."

United Nations Secretary-General Ban Ki-moon, in a statement dated September 5, urged Central Asian countries to negotiate on water management and said the World Bank report on Rogun would provide "informed guidance" for a decision on the Tajik project.

Catherine Ashton, the European Union's foreign policy chief, said in a separate statement on September 4 that any major infrastructure project should be undertaken only if supported by credible, independent studies.

Kyrgyz presidential adviser Farid Niyazov told Reuters the country was prepared to sign up to "the relevant agreements".

"Projects will undergo the most meticulous studies and thorough checks for security. It's in our interests too," he told Reuters on Friday.

(Additional reporting by Dmitry Solovyov in Almaty, Roman Kozhevnikov in Dushanbe and Olga Dzyubenko in Bishkek; Writing by Robin Paxton; Editing by Louise Ireland)