WASHINGTON (CNN) -- The head of the United Nations' nuclear watchdog group said Monday his inspectors are making progress determining the extent of Iran's nuclear program, but not nearly as quickly as he would like.Mohamed ElBaradei, director general of the International Atomic Energy Agency, said there is "a sea change" in understanding "the extent of the nature" of Iran's program.Speaking to a nonproliferation conference sponsored by the nonprofit Carnegie Endowment for International Peace, he complimented the Iranians for allowing access to facilities beyond the confines of the IAEA's mandate.Just last week, IAEA inspectors visited the Parchin military complex near Tehran, where environmental samples were taken. Unlike a previous visit, inspectors did not face restrictions on what buildings they could enter.There is, however, one more location the agency wants to visit. ElBaradei said Iran should allow inspectors to tour the Lavizan facility, where high-explosive tests are conducted."We are moving in the right direction," said ElBaradei, but he called on Iran to give the IAEA more legal authority, providing more transparency on the nature of its nuclear program.This weekend Iran indicated it is ready to resume the stalled negotiations with three European nations seeking to prevent Iran from obtaining a nuclear enrichment program, which could be used to make weapons. The United States has supported the efforts by those nations -- Britain, France and Germany. Iran's chief nuclear negotiator has contacted the three nations to restart talks, Iranian state-run news agency IRNA said Sunday. (Full story)Ali Larijani, secretary of Iran's Supreme National Security Council, wrote to leaders of Britain, France, and Germany emphasizing "the necessity of conducting negotiations," the report said.Iran broke off talks with the so-called EU-3 earlier this year, saying the demand that it stop its nuclear program altogether was unacceptable.Iran insists its program is purely for energy purposes, but the United States argues Iran is using the program as a guise to try to develop nuclear weapons.U.N. Secretary-General Kofi Annan had planned to visit Iran this month, in a trip largely aimed at restarting the stalled talks.But Annan canceled the trip after Iranian President Mahmoud Ahmadinejad's recent assertion that Israel should be "wiped off the map." Annan expressed "dismay" last week over the remarks in a rare rebuke of a U.N. member state. (Full story)