"We think they do, quite frankly," Mullen told CNN when asked whether Iran "might now have enough fissile material to make a bomb."

"Iran having a nuclear weapon, I believe, for a long time, is a very, very bad outcome for the region and for the world," Mullen said.

But later his spokesman clarified that the Admiral was referring to "low grade" material which would have to be high enriched.

CNN said Mullen was travelling and could not be reached immediately to clarify his statement.

Defence Secretary Robert Gates, speaking yesterday on NBC's 'Meet the Press', said of Iran, "They're not close to a stockpile, they're not close to a weapon at this point and so there is some time."

However, CNN said an IAEA official cautioned against drawing such dramatic conclusions from the data, saying Iran's stock of low-enriched uranium would have to be turned into highly enriched uranium to qualify as weapons-grade material. That hasn't been done, the official said.

Mullen's spokesman Capt. John Kirby told CNN on Sunday that "There are two components here: having enough and having it highly enriched."

"The chairman concurs Iran has enough low-enriched to produce a nuclear weapon, but it's important to note it's low-grade, and to enrich it would take time," Kirby said.

Iran tested its first nuclear power plant on Wednesday.

In the test at the Bushehr nuclear power plant, "dummy" fuel rods were used, so no nuclear reaction began.

Iranian officials said the next test will use enriched uranium, but it's not clear when the test will be held or when the facility will be fully operational.