Iran, France, Germany and Britain head back to the negotiating table next week - with the Europeans set to press Tehran to reach an agreement on its nuclear program. 

The United States is not scheduled to take part in the talks, but backs European efforts to reach a long-term solution.  The U.S. government says it is Iran's responsibility to prove to the world that it doesn't have nuclear weapons capabilities. 

The United States accuses Iran of secretly developing a nuclear weapons program and lying to International Atomic Energy Agency inspectors about it.  Iran denies these charges and says its nuclear program is only designed to generate electricity.

State Department spokesperson Richard Boucher says the burden is on Iran to show the world that it means what it says. “Iran claims it doesn't want a nuclear weapon,” he said.  “They should be going out of their way to demonstrate to the world, to show the world with confidence that is true.  They've been found for 20 years in covert programs.”

The IAEA says Iran has hidden nuclear activities for almost 20 years.  Agency Chief Mohamed ElBaradei has called on Iran to provide a full accounting of its nuclear activities to IAEA inspectors, but it's unclear if Iran will cooperate. 

Earlier this week Iran threatened to break seals put in place by IAEA inspectors and test essential parts for machines for nuclear work.  Meanwhile, satellite images indicate that Iran has begun construction on a second nuclear facility, which could be used to produce bomb-grade plutonium. 

Western diplomats close to the IAEA said Friday that Iran is building deep tunnels to store nuclear material at a site where it is known to have carried out uranium enrichment activities.  They speculate the tunnels are to hide and protect nuclear components from a possible aerial strike by the United States or Israel. 

State Department spokesperson Richard Boucher said these all fit into the pattern that Iran has followed over the years, to say one thing and do another. 

"There are repeated situations where Iran has been found to not be disclosing the whole truth about its programs, which continues to raise questions about Iran,” he added.  “And so rather than making statements that raise further questions about their intentions, one would think that if Iran were really sincere about what it has promised, they would be going out of their way to show that they were not seeking a nuclear weapon.  They would be going out of their way to build confidence in the international community."
 
After meeting with European leaders late last month, President Bush said they all agree that Iran should not have nuclear weapons.  There is speculation that the Bush Administration may agree to drop its opposition to Iran joining the World Trade Organization if Tehran agrees to dismantle its nuclear weapons program.