The trilateral meeting that involves the United States, Iran and the European Union (EU) continued in Muscat, the capital of Oman, on Monday to discuss core issues on Iran's nuclear program.
The two-day meeting, attended by U.S. Secretary of State John Kerry, Iranian Foreign Minister Mohammad-Javad Zarif and EU adviser Catherine Ashton, comes just two weeks before the Nov. 24 deadline for a comprehensive deal on the controversial nuclear program of Iran.
The Western sanctions against Iran and the country's uranium enrichment capacity are now the two key issues of the tough negotiations. No statement has been made by U.S. or Iranian officials after Sunday's meeting.
The meeting is part of the EU-coordinated negotiations between Iran and the P5+1 group, including Britain, China, France, Russia, the United States plus Germany.
Iran and the P5+1 group will hold another round of nuclear talks in Muscat on Tuesday, Omani officials said.
In a TV interview on Sunday, U.S. President Barack Obama said a "big gap" remains on how the West can have "verifiable, lock-tight assurances" that Iran cannot obtain nuclear weapon.
Prior to the Muscat meetings, Iran's senior nuclear negotiator Abbas Arachi said the talks in Oman are not likely to result in an agreement, Iran's official IRNA news agency reported on Saturday. However, he said reaching a final deal with powers over Iran's nuclear issue is "not difficult" before the Nov. 24 deadline.
The meetings in Muscat also follow media reports that Obama has written to Iran's Supreme Leader Ayatollah Ali Khamenei to express "shared interest" in fighting the Islamic State extremist group in Iraq and Syria. U.S. Secretary of State John Kerry, however, said in Beijing on Saturday that there was no linkage between the nuclear talks and the fight against the Islamic State.
After the deal between Iran and the P5+1 group on Nov. 24 last year, both sides have held several rounds of talks trying to work out a final agreement.
Under the interim deal agreed in Geneva last November, Iran agreed to suspend some sensitive nuclear activities in exchange for a limited sanction relief within 12 months to buy time for the diplomatic efforts.
The West wants Iran to significantly scale back its nuclear program to address its concern of proliferation risk, while Iran insists that its nuclear right is inalienable.