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TEHRAN, Oct 16 (Reuters) - Russian President Vladimir Putin said on Tuesday any use of military force in the Caspian region was unacceptable and Russia backed dialogue in resolving differences.

"We should not even think of making use of force in this region," Putin told a summit of the five Caspian Sea countries including Iran, which is defying Western pressure to halt its sensitive nuclear programme.

"We need to agree that using the territory of one Caspian Sea (state) in the event of aggression against another is impossible," he told the other leaders at the start of a one-day meeting in the Iranian capital.

The summit in Tehran is focused on resolving differences over sharing out the resources of the oil-rich Caspian Sea but Russian officials say Putin's bilateral talks with Iran will focus on Iran's nuclear standoff with the West.

The United States, leading efforts to isolate Tehran over work Washington suspects is aimed at developing nuclear bombs, says it would prefer a diplomatic solution to the dispute but has not ruled out military action if that were to fail.

Russia, saying it has no evidence that Tehran is seeking to build atom bombs, says force should not be an option in the nuclear row.

"It is important that we say that it is impossible to offer our territory to third countries in case of aggression or military action against one of the Caspian states," Putin said.

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