Brasilia: US Secretary of State Hillary Clinton has said the "burden of action" falls on Iran to prove it is serious in nuclear talks, dismissing Iranian appeals for world powers to ease sanctions first.

"The burden of action falls on the Iranians to demonstrate their seriousness and we're going to keep the sanctions in place and the pressure on Iran" as they prepare for new talks in Baghdad in May, Clinton said on Saturday.

"And we'll respond accordingly," Clinton said at a press conference with Brazilian Foreign Minister Antonio Patriota.

Iranian Foreign Minister Ali Akbar Salehi on Saturday called on the West to look to lifting its sanctions if it wants to quickly resolve the showdown over Tehran's disputed nuclear activities.

He hinted Iran could make concessions on uranium enrichment in return. Clinton said the United States is prepared for reciprocal action, but not right now.

"I believe in action for action," the chief US diplomat said.

But she said Iran must first address the concerns of the international community about its nuclear program, which the West suspects masks a drive to build a nuclear bomb. Iran insists its program is entirely peaceful.

"There has to be evidence by Iran that they would be seriously moving for removing a lot of their nuclear ambiguity that exists now," she said.