Sept. 18 (Bloomberg) -- President Mahmoud Ahmadinejad said Iran will pursue its nuclear program, defying demands to curb the work three days after the United Nations said the country isn't cooperating with a probe into possible weapons development.

``The nuclear issue is over,'' Ahmadinejad said today at a Tehran news conference broadcast live by state television. ``Pressure will not have an impact on the determination of the Iranian people'' to carry on with atomic research, he said.

Iran refused to answer questions about possible nuclear- weapons activity and expanded its production of atomic fuel at a facility in Natanz, the UN's International Atomic Energy Agency said in a report published Sept. 15.

Iran's defiance increased tension between the Persian Gulf country and Western powers over the program, which the U.S. and some major allies say is cover for weapons development. The government in Tehran faces further isolation, the U.S. said following the IAEA report, while France said it will back moves for a fourth round of UN sanctions against the country.

The UN Security Council has repeatedly called on Iran to halt its enrichment of uranium, a process that can fuel a nuclear power station or form the core of a bomb.

Iran says its program is for civilian use, intended to generate electricity, and legal under the nuclear Non- Proliferation Treaty, to which it is a signatory.

The State Department said Sept. 16 that U.S., U.K., French, Chinese, Russian and German diplomats will discuss the dispute tomorrow, ahead of the UN General Assembly in New York next week. Those countries' foreign ministers are scheduled to talk about possible further steps in the dispute at the Assembly. Ahmadinejad is due to attend the UN gathering.

Further Sanctions

China indicated Sept. 16 that it may not be prepared to back further sanctions, with Foreign Ministry spokeswoman Jiang Yu saying that negotiation was ``the only way'' to resolve the dispute.

Tension with the West over the war in Georgia has sharpened Russian opposition to pressuring Iran at the UN, U.S. and British envoys said last week. China and Russia are both veto-wielding, permanent members of the Security Council.

To contact the reporter on this story: Ladane Nasseri in Tehran at lnasseri@bloomberg.net.