The United States has intelligence that Iran is working to adapt missiles to deliver a nuclear weapon, further evidence that the Islamic republic is determined to acquire a nuclear bomb, Secretary of State Colin L. Powell said Wednesday.

Separately, an Iranian opposition exile group charged in Paris that Iran is enriching uranium at a secret military facility unknown to U.N. weapons inspectors. Iran has denied seeking to build nuclear weapons.

"I have seen some information that would suggest that they have been actively working on delivery systems. . . . You don't have a weapon until you put it in something that can deliver a weapon," Powell told reporters traveling with him to Chile for an Asia-Pacific economic summit. "I'm not talking about uranium or fissile material or the warhead; I'm talking about what one does with a warhead."

Powell's comments came just three days after an agreement between Iran and three European countries -- Britain, France and Germany -- designed to limit Tehran's ability to divert its peaceful nuclear energy program for military use. The primary focus of the deal, accepted by Iran on Sunday and due to go into effect Nov. 22, is a stipulation that Iran indefinitely suspend its uranium enrichment program.

The issue of adapting a missile is separate from the question of enriching uranium for use in a weapon.

"I'm talking about information that says they not only have these missiles, but I am aware of information that suggests that they were working hard as to how to put the two together," Powell said, referring to the process of matching warheads to missiles. He spoke to reporters during a refueling stop in Manaus, Brazil.

"There is no doubt in my mind -- and it's fairly straightforward from what we've been saying for years -- that they have been interested in a nuclear weapon that has utility, meaning that it is something they would be able to deliver, not just something that sits there," Powell said.

Iran has long been known to have a missile program, while denying that it was seeking a nuclear bomb. Powell seemed to be suggesting that efforts not previously disclosed were underway to arm missiles with nuclear warheads.

Joseph Cirincione, director of the Non-Proliferation Project at the Carnegie Endowment for International Peace, said Powell's remarks indicated that Iran was trying to master the difficult technology of reducing the size of a nuclear warhead to fit on a ballistic missile.

"Powell appears to be saying the Iranians are working very hard on this capability," Cirincione said. He said Powell's comments were striking because the International Atomic Energy Agency said this week that it had not seen any information that Iran had conducted weapons-related work.

In a 32-page report, IAEA chief Mohamed ElBaradei wrote that "all the declared nuclear material in Iran has been accounted for, and therefore such material is not diverted to prohibited activities," such as weapons programs. But ElBaradei said that he could not rule out the possibility that Iran was conducting a clandestine nuclear weapons program.

Powell also told reporters that the United States had not decided what action to take following Sunday's agreement. The Bush administration had insisted that Iran's past violations warranted taking the matter to the U.N. Security Council.

Powell said the United States would monitor verification efforts "with necessary and deserved caution because for 20 years the Iranians have been trying to hide things from the international community."

Meanwhile, in Paris, the exile group charged that Iran was still enriching uranium and would continue to do so despite the pledge made Sunday to European foreign ministers. The group, the National Council for Resistance in Iran, or NCRI, also claimed that Iran received blueprints for a Chinese-made bomb in the mid-1990s from the global nuclear technology network led by the Pakistani scientist Abdul Qadeer Khan. The Khan network sold the same type of bomb blueprint to Libya, which has since renounced its nuclear ambitions.

Mohammad Mohaddessin, chairman of the foreign affairs committee of the Paris-based NCRI, told reporters at a news conference that the Khan network delivered to the Iranians a small quantity of highly enriched uranium that could be used in making a bomb. But he said the amount was probably too small for use in a weapon.

The NCRI is the political wing of the People's Mujahedeen organization, which the State Department has labeled a terrorist organization. The NCRI helped expose Iran's nuclear ambitions in 2002 by disclosing the location of the government's secret uranium enrichment facility at Natanz. But many of its subsequent assertions about the program have proven inaccurate.

On Wednesday, Mohaddessin used satellite photos to pinpoint what he said was the new facility, inside a 60-acre complex in the northeast part of Tehran known as the Center for the Development of Advanced Defense Technology. The group said that the site also houses Iranian chemical and biological weapons programs and that uranium enrichment began there a year and a half ago, to replace a nearby facility that was dismantled in March ahead of a visit by a U.N. inspections team.

The group gave no evidence for its claims, but Mohaddessin said, "Our sources were 100 percent sure about their intelligence." He and other group members said the NCRI relies on human sources, including scientists and other people working in the facilities and locals who might live near the facilities and see suspicious activities.

The IAEA, the U.N. nuclear monitoring body, had no immediate comment on the claims but said it took all such reports seriously.

The agency has no information to support the NCRI claims, according to Western diplomats with knowledge of the U.N. body's investigations of Iran.

Some diplomats and arms control experts privately discounted the Iranian group's latest claim, saying it appeared designed to undermine the deal that the Tehran government signed with Britain, France and Germany. In Tehran on Wednesday, Iranian officials said they considered the enrichment suspension temporary and contingent upon a favorable decision at the IAEA meeting next week and on quick progress in talks next month on long-term guarantees that Iran can apply nuclear technology for peaceful purposes.

Richburg reported from Paris. Staff writers Glenn Kessler and Dafna Linzer in Washington contributed to this report.

Mohammad Mohaddessin, of the National Council for Resistance in Iran, uses satellite imagery to pinpoint what the group says is a previously unknown nuclear facility in Iran.