Republican presidential candidate Donald Trump said it would be hard to "rip up" the United States-led agreement with Iran on its nuclear program, but that if he was elected president he would "police that contract so tough they don't have a chance."

In an interview on NBC's "Meet the Press" on Sunday, the real estate mogul described the team that negotiated the agreement, including Secretary of State John Kerry, as "incompetent."

Nevertheless, it would be "very tough" to rip up the deal, he said, as some critics have called for. But "I'm really good at looking at a contract," Trump said, and "as bad as the contract is, I will be so tough on that contract."

The agreement reached by Iran and the United States and other world powers on July 14 would give Iran some relief from economic sanctions in return for strict limits on its nuclear program.

The sanctions relief could give Iran access to some $150 billion, which Trump said he would never have allowed Iran to have, had he been negotiating the deal.

It will make Iran such a wealthy, powerful nation that it will gain nuclear weapons and "take over parts of the world that you wouldn't believe," he said. "I think it's going to lead to nuclear holocaust."

Congress has until Sept. 17 to accept or reject the pact. President Barack Obama has said the deal is the best option for achieving stability in the Middle East and that scuttling it would be a historic mistake.

(Reporting by Toni Clarke in Washington, editing by Larry King)