"President Obama needs consistency to promote mutual confidence," Mohammad Javad Zarif said in a tweet. "Flip-flop destroys trust and undermines US credibility."
His remarks came after Obama told visiting Israeli Prime Minister Benjamin Netanyahu that the use of force was still on the table in dealing with Iran's controversial nuclear programme.
"We take no options off the table, including military options, in terms of making sure that we do not have nuclear weapons in Iran," Obama said, just days after his historic call with Iranian President Hassan Rouhani spurred hopes of a diplomatic breakthrough in the decade-long standoff.
But he has also said that Iran should retain the right to a "peaceful" civilian nuclear energy programme after doing so.
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In the meeting yesterday, Netanyahu warned that sanctions must be maintained against Tehran and even strengthened if necessary, saying Iran had agreed to negotiate because of the punitive measures -- which have hurt its economy badly.
Zarif was critical of the notion.
Obama's "presumption that Iran is negotiating because of his illegal threats and sanctions is disrespectful of a nation, macho and wrong," he said in another post on his Twitter account.