Santiago, Chile ? 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 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.

“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 were under way, not previously disclosed, 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 released this week, 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 there he could not rule out the possibility that Iran was conducting a clandestine nuclear weapons program.