U.S. defense officials said Wednesday that Iran can produce enough highly enriched uranium ( HEU) for a nuclear bomb in one year, but needs three to five years to assemble one.

During a Congressional hearing on U.S. policy towards Iran, Ronald Burgess, director of Defense Intelligence Agency, told lawmakers that the Pentagon estimates Iran can have enough HEU for a nuclear bomb in a year's time.

"The general consensus ... is we're talking one year," said Burgess. The estimate is based on Iran's centrifuges that the United States has "visibility into."

Another witness, James Cartwright, vice chairman of Joint Chiefs of Staff, told the Senate Armed Services Committee that the timeframe for Iran to assemble a nuclear bomb would be "three to five years."

"I can't tell you what problems they will encounter ... with the highly enriched uranium, you're still dealing in three to five years to create a weapon," he said.

Cartwright said the production of enough HEU and assembling of a weapon can be either sequential or simultaneous.

The West has been accusing Iran of seeking to build a nuclear weapon, but Iran insists its nuclear program is for peaceful purposes. The United States is pushing for more sanctions on Iran.