Iran says it has started small-scale uranium enrichment - an initial step in the process of producing fuel for civilian nuclear reactors or atomic weapons.
Top Iranian nuclear official Javad Vaeidi told reporters in Tehran Tuesday that work has resumed at the Natanz nuclear plant. He did not elaborate.
Earlier, diplomats at the Vienna-based International Atomic Energy Agency said Iranian technicians have fed uranium gas into centrifuge machines for enrichment.
IAEA inspectors are due to visit the plant today to assess its research activities.
Tehran had warned it would resume large-scale enrichment activities after the IAEA decided earlier this month to refer the Iranian nuclear issue to the U.N. Security Council.
U.N. Secretary-General Kofi Annan, who met with President Bush in Washington Monday, says he hopes there will be no steps to "escalate the situation."
Iran denies Western charges that it is trying to build atomic weapons.Some information for this report was provided by AFP, AP and Reuters.