Attacking the Bush administration's handling of Iraq on Wednesday, Kerry also said it was time for President George Bush to acknowledge his difficulties in managing Iraq to the world.
"They are doing it in such a frankly inept way," Kerry said.
Set to challenge Bush in November presidential elections, Kerry urged the US-led occupation authority to hand over responsibility in Iraq to a "legitimate international entity".
He added: "People don’t want to go to work for Paul Bremer – the US administrator in Baghdad.
"I am not the president and I did not create this mess, so I don’t want to acknowledge a mistake that I have not made," Kerry said.
"I am not the president and I did not create this mess, so I don’t want to acknowledge a mistake that I have not made"
Democratic presidential contender
"But the president needs to step up and acknowledge that there are difficulties and that the world needs to be involved, and they need to reverse this policy," he said.
Kerry said Bush had blundered by excluding countries that opposed the Iraq war from the huge rebuilding contracts. "That's a terrible message to send to countries."
"They need to go to the world and say: 'We are not going to have an American authority that is creating this new government, we are going to have an international authority that will help develop the new government,'" the presidential contender said.
Kerry's criticism comes two days after leading Democratic Senator Ted Kennedy likened the US-occupation of Iraq as "Bush's Vietnam".
Meanwhile, another prominent Democratic senator has opposed moves to send more US troops to Iraq as reinforcements.
"At this juncture, more US forces in Iraq equates to more US targets in Iraq," Robert Byrd said.