US President Barack Obama renewed his administration's offer of dialogue and diplomacy with Tehran on Saturday, a year after his offer of a new beginning with Iran failed to achieve concrete results.

Obama, who addressed Iranians in a new videotaped appeal to mark the observance of Nowruz -- an ancient festival celebrating the arrival of spring -- has pledged to pursue aggressive sanctions to prevent Iran from getting a nuclear weapon.

"We are working with the international community to hold the Iranian government accountable because they refuse to live up to their international obligations," Obama said in the address, according to excerpts released by the White House.

"But our offer of comprehensive diplomatic contacts and dialogue stands," he said.

Iran, which has refused to halt its uranium enrichment program, denies it is seeking to build a nuclear bomb and says its nuclear program is aimed at generating electricity.

Obama said Washington was committed to a "more hopeful" future for the Iranian people despite US differences with Iran's government.

During his first year in office, Obama marked Nowruz with a then-unprecedented message offering Iran a "new beginning" of diplomatic engagement with the United States.

But Tehran rebuffed Obama's gesture and relations soured further when Iranian authorities cracked down on opposition protesters after a disputed election last June, drawing US condemnation.

"Over the course of the last year, it is the Iranian government that has chosen to isolate itself, and to choose a self-defeating focus on the past over a commitment to build a better future," Obama said.

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