"We are celebrating together Nowruz today and promoting the Nowruz banner as one of justice, freedom, equality and fraternity among all countries," Jalal Talabani, the Iraqi president, said.
Ahmadinejad, whose policies have served to increase Iran's international isolation, talked of "collective cooperation" among countries of the bloc.
"It is a cause of joy that through collective co-operation Nowruz became global," he said.
Barack Obama, the US president, delivered a video address to Iranians on the occasion of Nowruz, which fell on March 21, this year and also last year in which he offered dialogue with Tehran to resolve longstanding political conflicts.
Ayatollah Ali Khamenei, Iran's supreme leader, and Ahmadinejad have so far avoided a direct response to the offer.