WASHINGTON - US President Barack Obama on Thursday urged the people and leaders of Iran to seize the "historic" opportunity presented by nuclear talks and remake long-troubled ties between the two countries.
In a video message directed at Iranians celebrating the new year festival of Nowruz, Obama said that "we have the best opportunity in decades to pursue a different future between our countries."
Negotiators in Switzerland are approaching the final stages of an agreement that would have Iran scale back its nuclear programme in return for relief from sanctions.
But Obama's Republican foes, allies Israel and in the Gulf - as well as hawks in Tehran - have voiced opposition to the agreement.
"There are people in both our countries and beyond who oppose a diplomatic resolution," Obama said.
"My message to you - the people of Iran - is that together we have to speak up for the future we seek.
"The days and weeks ahead will be critical. Our negotiations have made progress, but gaps remain."
Obama's video was subtitled in Farsi and included a direct appeal to Iran's large and youthful population, many of whom have known only antagonism between the United States and Iran.
The 1979 Iranian revolution and subsequent capture of US embassy hostages in Tehran led to a rupture in diplomatic relations that is only now starting to be repaired.
Iran's Islamic leaders are accused of seeking a nuclear weapon - which they deny - have supported groups like Hezbollah and have called for the destruction of Israel.
"I believe that our nations have an historic opportunity to resolve this issue peacefully, an opportunity we should not miss," Obama said.
"A nuclear deal now can help open the door to a brighter future for you, the Iranian people, who as heirs to a great civilisation have so much to give to the world.
"For decades, our nations have been separated by mistrust and fear. Now it is early spring.
"Now it is up to all of us, Iranians and Americans, to seize this moment and the possibilities that can bloom in this new season."