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.