The US has accused Iran of bullying foreign diplomats, in an escalating row over Tehran's nuclear ambitions.
Khatami called the resolution 'very bad'
US diplomat Kenneth Brill said Iran's president was using "intimidation" by saying Tehran might resume its uranium enrichment programme.
President Mohammad Khatami rejected a draft before the International Atomic Energy Agency which "deplores" Iran's lack of co-operation on nuclear inspections.
Iran denies US accusations that it is secretly developing nuclear weapons.
'Something to hide'
Mr Brill, the US Ambassador to the United Nations in Vienna, said: "This full-blown effort to try to change the direction of the [IAEA] board through public and private intimidation suggests Iran has something to hide."
"People who are trying to produce electricity for light bulbs don't engage in this kind of behaviour," he added, referring to Iran's position that it only wants to use nuclear technology to generate power.
He was responding to Mr Khatami's rejection of a toughly worded resolution being considered in Vienna this week by IAEA members.
"If this resolution passes, Iran will have no moral commitment to suspend uranium enrichment," Mr Khatami said.
"The IAEA resolution is very bad... [it] violates our country's rights.
International pressure made Iran open up to nuclear inspections
"If it passes, in the future we will have more problems with co-operating with the agency."
But he added that Iran had no intention of withdrawing from the nuclear Non-Proliferation Treaty, as North Korea has done.
The BBC's Jim Muir says officials in Tehran are angry, arguing that they have met all their commitments.
They claim Britain, France and Germany - the countries behind the latest resolution - are acting under pressure from Washington.
Our correspondent says in the past, Iran has continued to co-operate despite some tough rhetoric.
But with a new conservative-dominated parliament, there is no guarantee that will continue, he says.
The draft resolution does not contain any deadline or trigger mechanism to set into motion possible sanctions on Iran.
Washington has been pushing for the IAEA to report Tehran to the UN Security Council, which could lead to formal sanctions.
An IAEA report published in April said suspicions still hung over Iran's nuclear programme.
It said the discovery of bomb-grade uranium traces at Iranian facilities, and an Iranian attempt to buy centrifuges to speed up the enrichment of uranium, were a cause for concern.
Under growing international pressure, Iran says it has suspended uranium enrichment and has allowed the IAEA to inspect its nuclear facilities without notice.