Work has stopped at the plant because of financing problems according to the Russian contractors.
Although Russia has backed two rounds of punitive UN sanctions against Iran over its nuclear ambitions, Moscow says engagement is a more effective way of tackling the situation.
But Putin has travelled to Tehran to attend a summit of the five states that surround the Caspian Sea and on Tuesday issued a warning that none of the states bordering the world's largest lake should allow their territory to be used for military action against another coastal state.
This was an apparent response to talk in the West about military strikes on Iran.
"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 the one-day meeting.
His comments appear directed towards close US allies, Azerbaijan which borders the Caspian and nearby Turkey.
Putin's trip had been overshadowed by rumours that he might be the target of an assassination attempt.
The Russian Interfax news agency reported on Sunday that Putin had been advised of an assassination plot against him that was to take place during his visit to Tehran.
But Putin refused to cancel his visit, saying the security services "must do their work".
"If you react to various threats and recommendations of the security services, then you should sit at home".
Earlier Tehran described reports of a plot against Putin as "totally baseless".
Putin is the first Kremlin leader to travel to Iran since Josef Stalin, the former Soviet leader, attended a wartime summit with Winston Churchill, former British prime minister, and Franklin Roosevelt, former US president, in 1943.
Putin said on Monday that negotiation was the best tool for dealing with Iran and trying to intimidate Tehran was "hopeless".
"But to demonstrate patience and look for a way out is possible and should be done," he said.
"If we have a chance to keep up these direct contacts, then we will do it, hoping for a positive, mutually advantageous result."
Russia has sold weapons to Iran, in defiance of US concerns, and is building a nuclear power station at Bushehr.
|Putin, right, is the first Russian leader to visit Iran since 1943 [AFP]|
Source: Al Jazeera and agencies