TEHRAN, Iran — President Putin of Russia issued a veiled warning yesterday against any attack on Iran as he began the first visit by a Kremlin leader to Tehran in six decades — a mission reflecting Russian-Iranian efforts to curb American influence.

He also suggested Moscow and Tehran should have a veto on Western plans for new pipelines to carry oil and natural gas from the Caspian Sea, using routes that would bypass Russian soil and break the Kremlin’s monopoly on energy deliveries from the region. Mr. Putin came to Tehran for a summit of the five nations bordering the Caspian, but his visit was aimed more at strengthening efforts to blunt American economic and military ties in the area. Yet he also refused to set a date for completing Iran’s first nuclear reactor, trying to avoid an outright show of support for Iran’s defiance over its nuclear program.

Mr. Putin strongly warned outside powers against use of force in the region, a clear reference to America, which many in Iran fear will attack over the West’s suspicions that the Iranians are secretly trying to develop nuclear weapons.

President Ahmadinejad of Iran made similar comments.

“We are saying that no [Caspian] nations should offer their territory to outside powers for aggression or any military action against any of the Caspian states,” Mr. Putin said.

The five national leaders at the summit later signed a declaration that included a similar statement — an apparent reflection of Iranian fears that America could use Azerbaijan’s territory as a staging ground for military strikes in Iran. Mr. Putin has warned against such attacks previously, but reiterating them in Tehran gave them greater resonance — particularly at a summit for a region where Moscow deeply resents American and European attempts at greater influence.