Iran declared its refusal Tuesday to discuss its nuclear program -- including the disclosure of a second nuclear enrichment plant -- when it sits down at the negotiating table Thursday with the five permanent members of the U.N. Security Council and Germany, Reuters reported. A top Iranian official told the news agency that his country will not abandon its nuclear activities, "even for a second."

Iran's nuclear chief also announced Tuesday that his country built its newly revealed uranium enrichment facility inside a mountain and next to a military site to ensure continuity of its nuclear activities in case of an attack.  The revelation comes as the Obama administration works up plans to push for new sanctions against the country, targeting its energy, financial and telecommunications sectors if it does not comply with international demands to come clean about its nuclear program, U.S. officials said Monday.

The officials said the U.S. would expand its own penalties against Iranian companies and press for greater international sanctions against foreign firms, largely European, that do business in the country unless Iran can prove that its nuclear activities are not aimed at developing an atomic weapon.

Among the ideas being considered are asset freezes and travel bans against Iranian and foreign businesses and individuals who do business in those areas, the officials said. The officials spoke on condition of anonymity because the measures were still under review.

The proposed sanctions would largely focus on investment in Iran's energy infrastructure and development, the officials said. Until now, the sanctions have dealt mainly with companies and people suspected of buying or selling weapons of mass destruction or their components.

Diplomats from the five permanent members of the U.N. Security Council -- Britain, China, France, Russia and the United States -- and Germany meet with Iran's top nuclear negotiator on Thursday to press once again an offer of incentives for Iran to halt suspect activity.

But U.S. officials familiar with the process that dates back to the Bush administration are skeptical that Iran will agree to demands to fully disclose its intentions. Iran repeatedly has denied it wants the bomb and that its nuclear program is for peaceful purposes only.

Previous meetings -- the last in July 2008 -- have not made progress and the officials said they did not think Thursday's talks in Geneva would produce any significant developments on the nuclear front.

Instead, the officials said they expected Iran to raise a broad range of global political concerns while the other participants focused on Iran's nuclear program, including the disclosure last week of a new uranium enrichment facility.

The officials, who spoke on condition of anonymity due to the sensitive nature of the talks, said they believed another round of talks would be scheduled before mid-November, at which Iran would face demands to address the international community's concerns.

If they refuse, the officials said the U.S. and its partners would move ahead with new penalties.

The Associated Press contributed to this report.