The chief U.N. nuclear monitor urged Iran (search) on Monday to bare its nuclear secrets, saying complete transparency was the only way to convince the world it was not making nuclear weapons.

Mohamed ElBaradei (search) spoke to The Associated Press ahead of a key trip to Tehran where he hopes to persuade the government to clear up troubling questions about its nuclear programs.

The United States has been at the forefront of accusations that Iran is running a clandestine weapons program. President Bush warned last month that Iran must keep its promise not to develop nuclear weapons. If the Iranians don't, "we will deal with that," Bush said.

Iran denies it wants nuclear weapons, and it has already let the International Atomic Energy Agency (search) inspect parts of its programs.

But ElBaradei, who heads the agency, wants Iran to let it make more intrusive checks.

Iran needs "to give us additional authority for the international community to be fully satisfied that the program is completely dedicated to peaceful purposes," said ElBaradei, who is scheduled to meet with officials in Tehran on Wednesday.

ElBaradei also is seeking permission to conduct environmental sampling to see if suspect radioactive material was used at one site. Diplomats familiar with his itinerary said he would seek a commitment from Tehran to hold off using materials and technologies that can be used to make nuclear weapons until all concerns are laid to rest.

Some of these technologies and materials can be used either for peaceful or military purposes, underscoring the need for Iran to allow the agency more oversight, ElBaradei said.