The offer was transmitted on Friday by the ambassadors of Britain, France and Germany, the so-called EU-3 which has been negotiating with Iran to seek guarantees that its nuclear programme is peaceful.
Meanwhile, Tehran has said the European Union has offered to support it as the main transit route for oil and gas from Central Asia as part of a package of incentives meant to persuade it to freeze its nuclear activities.
"In the proposal, they have supported the idea of Iran being the main energy transit route to Europe from Central Asia," a senior Iranian close to the EU negotiations told Reuters on Friday.
Iran repeatedly threatened this week to resume uranium processing, a move that would end two years of talks and could lead to its referral to the UN Security Council for possible sanctions.
Earlier, Britain, Germany and France had submitted proposals to Iran for economic and political cooperation meant to persuade it to abandon all activities that might be used to make a nuclear bomb.
The three European Union countries are also planning to call a meeting of the International Atomic Energy Agency -- the UN's nuclear watchdog -- early next week to warn Tehran against restarting sensitive nuclear work, diplomats said.
Iran says it aims only to generate electricity and has a right to a peaceful nuclear programme.