The US ambassador to the UN says the Obama administration would engage in direct "vigorous" diplomacy with Iran over its nuclear program.

Shortly after a meeting with Secretary-General Ban Ki-moon on her first day in office, Susan Rice said Barack Obama's administration "look forward to engaging in vigorous diplomacy that includes direct diplomacy with Iran."

The administration of former US President had been pushing for a fourth round of UN sanctions against Iran over its nuclear activities to add to the three resolutions already issued.

Rice's Monday remarks come in stark contrast with the policies of the era of George W. Bush and in line with President Obama's pledge to enter into direct negotiations with Iranian leaders over the country's nuclear impasse.

During his inaugural address President Obama said Washington is ready to "extend a hand" to those willing "to unclench your fist".

Rice also went on to warn that, "Dialogue and diplomacy must go hand in hand with a very firm message from the United States and the international community that Iran needs to meet its obligations as defined by the Security Council."

The newly installed US envoy said Iran's refusal to take heed of Security Council resolutions - which call for the country to halt its enrichment activities - would force the international community to up pressure on the Islamic Republic.

"We will look at what is necessary and appropriate with respect to maintaining pressure toward that goal of ending Iran's nuclear program," Rice said.

The United States, the European Union and other Western powers accuse Iran of amassing the capability to produce a nuclear bomb.

Tehran, a signatory to the nuclear Non-Proliferation Treaty (NPT), denies the allegation, insisting its activities are directed at the civilian applications of the technology.

The UN agency pertinent to the Iranian nuclear program, the International Atomic Energy Agency (IAEA), said in its November and latest report that it has "been able to continue to verify the non-diversion of declared nuclear material in Iran".

The agency, however, argued that unless Tehran increases its cooperation with the agency, the UN body "will not be able to provide credible assurance about the absence of undeclared nuclear material and activities in Iran".

CS/HGH