TEHRAN, Iran (CNN) -- Iran should be allowed to pursue its nuclear program for peaceful purposes, Russian President Vladimir Putin said on Tuesday during the first visit to the country by a Kremlin leader since 1943.

Putin, right, is greeted by Iranian President Mahmoud Ahmadinejad following his arrival in Tehran.

Putin, who is in Tehran to attend a summit of Caspian Sea nations, said that he and the other leaders agreed that "peaceful nuclear activities must be allowed" in the region.

"The Iranians are cooperating with Russian nuclear agencies and the main objectives are peaceful objectives," he said.

Russia is building Iran's first nuclear power plant and has resisted moves by the U.S. and its allies to impose stronger U.N. sanctions against Tehran.

On Monday, U.S. Defense Secretary Robert Gates reiterated the Bush administration's stance that "all options" must be kept "on the table" in confronting the threats posed by Iran -- a reference to the option of using military action against the long-time U.S. adversary.

"We should have no illusions about the nature of this regime or its leaders -- about their designs for their nuclear program, their willingness to live up to their rhetoric, their intentions for Iraq, or their ambitions in the Gulf region," Gates said in a speech to the Jewish Institute for National Security Affairs.

The leaders of Iran, Russia, Kazakhstan, Turkmenistan and Azerbaijan also met Tuesday to reach agreement on issues relating to the sharing and regulating of the Caspian Sea -- the world's largest inland body of water.

Speaking afterwards, Putin said that no Caspian nation should offer its territory to third parties intent on military action against other countries in the region -- a reference to rumors that the U.S. planned to use Azerbaijan as a base for a possible attack against Iran, The Associated Press reported.

"We are saying that no Caspian nation should offer its territory to third powers for use of force or military aggression against any Caspian state," Putin said.

"The Caspian Sea is an inland sea and it only belongs to the Caspian states, therefore only they are entitled to have their ships and military forces here," added Iranian President Mahmoud Ahmadinejad.

Putin, defying reports of an assassination plot against him, was greeted by Iranian Foreign Minister Manouchehr Mottaki as he stepped off his plane at Tehran's Mehrabad Airport.

During a news conference Monday after talks with German Chancellor Angela Merkel in Wiesbaden, Germany, Putin said rumors of an attempt on his life would not stop his plans.

"Of course I will travel to Iran," Putin said. "If I reacted to these kinds of rumors every time, I could never leave the house."

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Iranian officials denied there was an assassination plot against Putin, with a Foreign Ministry spokesman describing rumors of a possible terrorist action during the Putin visit baseless.

"Spreading this kind of totally false news lacks any value and cannot damage the trend of the prepared programs," spokesman Mohammadali Hosseini told the Iranian FARS news agency.

Hosseini blamed the rumor on Western media, particularly the U.S. media, saying the report was "made up by the enemies of relations between Iran and Russia to create a psychological war."

Putin's visit is the first by a leader in the Kremlin to Iran since Joseph Stalin's World War II conference meeting with U.S. President Franklin D. Roosevelt and British Prime Minister Winston Churchill.

"Putin's trip to Tehran is a show of Russia's independence in global affairs. Putin, who approaches the end of his term, wants to demonstrate that he wouldn't cave in to the U.S. pressure," said Alexander Pikayev, an expert on Iran with Russia's Institute for World Economy and International Relations, in a report carried by AP.

Putin's schedule also includes meetings with Ahmadinejad and Iran's supreme leader, Ali Khamenei, AP said. E-mail to a friend

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