Iran said it will use domestically produced uranium concentrates for the first time at a key nuclear facility today, signaling determination to push ahead with its atomic work a day before talks with world powers.
The move appeared designed to show that Iran will not back down in a long-running dispute over its nuclear program ahead of the December 6-7 meeting in Geneva.
Iran says its nuclear program is aimed at power generation but the West suspects Tehran wants to make atom bombs.
Iran's nuclear energy chief, Ali Akbar Salehi, said the Islamic state was making rapid technological progress, despite tougher sanctions introduced by the United Nations and the West.
"No matter how much effort they put into their sanctions and in creating all sorts of hindrances our nuclear activities will proceed," he told a televised news conference.
Western powers want Iran to suspend uranium enrichment activity, which can have both civilian and military purposes. Tehran has ruled this out.
Western diplomats say the sanctions are hurting Iran's oil-dependent economy and they hope this will persuade it to enter serious negotiations about its nuclear program.
But analysts expect no breakthrough in Geneva, the first such meeting in over a year. At most, they believe, it may lead to more meetings.
Last week's killing of an Iranian nuclear scientist in Tehran, which Iran has blamed on Western intelligence services, may also cloud the atmosphere for dialogue in the Swiss city.