A draft resolution agreed by the U.N. Security Council's five members with veto power - the United States, France, Britain, China and Russia - and by Germany was sent to the 15-nation council for a vote.
It seeks new sanctions on Iran for refusing to suspend uranium enrichment, which can be used to generate power - as Tehran insists is its sole aim - but also in nuclear bombs.
Ahmadinejad, despite saying the council "had no legitimacy among nations", has asked to address it to defend Iran's right to nuclear technology when the issue comes to a vote.
The West fears Iran's atomic work is aimed at building atomic weapons but a leading Iranian cleric insisted on Tehran was being honest.
"We are not lying. Our atomic work is for serving the nation, not for building arms," Ayatollah Mohammed Emami-Kashani, a member of Iran's highest arbitration body the Expediency Council, said during a recent prayers sermon broadcast live on state radio.
In December the Security Council imposed trade sanctions on Iran's sensitive nuclear materials and technology, and froze assets abroad of some Iranian individuals and companies.
Iran ignored a February 21 deadline to suspend enrichment or face further action.
The new draft includes a ban on Iranian arms exports and a freeze on assets abroad of an expanded list of individuals and companies involved in Tehran's nuclear and ballistic missile programs.
It also calls for nations and institutions to bar new grants or loans to Iran except for "humanitarian and developmental" purposes. The sanctions would be suspended if Iran complied and returned to negotiations.
Russia, which has been helping build Iran's Bushehr nuclear power plant, reminded the Islamic Republic that it should pay up on time if it wants to see the project completed as scheduled in September.
"No one builds nuclear stations for free. We are not going to complete the construction of the station on our own account," Sergei Kiriyenko, head of Russia's state atomic agency Rosatom, told journalists.
Tehran denies there have been payment delays. Russia's involvement in Bushehr has clouded Moscow's relations with the West.