The United States is prepared to respond if Iran does not abide by its commitments over its controversial nuclear program, a top aide to US President Barack Obama has said.

"Iran now needs to follow through on its commitments," National Security Adviser James Jones said Tuesday.

"Nothing is off the table," Jones warned in a Washington speech to the liberal pro-Israel lobby group J Street, without specifying details of a possible response.

World powers have warned that Tehran could face a fresh round of tougher sanctions targeting its oil sector if it continues to defy international demands.

"We will see if engagement is able to produce the concrete results we need, and we'll be prepared if it does not," Jones said.

His comments came after Iranian state television said Tehran wanted "very important changes" to a UN-brokered nuclear fuel deal and would offer its formal response by Thursday. In a reversal from the more confrontational policy of his predecessor, Obama has sought to engage Iran diplomatically to thaw three decades of frozen ties.

"We also have a long, long way to go," the retired US general cautioned, noting that the Obama administration had consulted with Israel, as well as with members of the United Nations Security Council plus Germany.

Iran's state-owned English language Press TV earlier reported that Tehran will not shift its entire stock of low-enriched uranium abroad for refining, as hinted at by the proposed deal -- indicating that Iran would demand changes. Iranian officials meanwhile continued to express conflicting views on the draft deal. State Department spokesman Ian Kelly said it would be "unfortunate" if Iran rejected the deal, while refusing to rule out changes to the original accord.

Western officials hope the arrangement would strip the Islamic republic of any need to produce highly-enriched uranium, which they fear could be used as fissile material for a nuclear bomb.

"If implemented, this arrangement would set back the clock on Iran's breakout capability because it would reduce Iran's stockpile far below the amount needed for a weapon, and it would take time to reconstitute the amount needed for a breakout," said Jones.

"But there should be no doubt: suspension of Iran's enrichment program remains our goal."