By Arshad Mohammed and Parisa Hafezi
UNITED NATIONS (Reuters) - U.S. Secretary of State John Kerry said he saw an opportunity for progress this week towards ending Syria's four-year civil war as he met Iran's Foreign Minister Mohammad Javad Zarif on Saturday.
Western officials said Kerry wants to launch a new effort at the U.N. General Assembly to try to find a political solution to the Syrian conflict, which has taken on new urgency in light of Russia's military build-up in support of Syrian President Bashar al-Assad and a refugee crisis that has spilled into Europe.
The new U.S. approach, which officials stressed was in its infancy, could bring Russia, a major ally of Assad, together with countries such as Saudi Arabia, Turkey and that support Syrian opposition groups against Assad.
Former U.S. diplomats said any movement toward ending a conflict in which at least 200,000 people have died and millions more been displaced was likely to be slow at best given the divisions over Assad's future and over the threat posed by the Islamic State militant group that has seized swathes of Syria and Iraq.
It is unclear what role, if any, might be played by Iran, which is a long-standing supporter Assad. The United States has long said Assad must go, but in recent weeks has left open the possibility of his staying in power during a transition.
"We need to achieve peace and a way forward in Syria, in Yemen, in the region," Kerry told reporters as he posed for photographs with Zarif. "There are opportunities this week, through these discussions, to make some progress."
Syria was also likely to come up at Kerry's scheduled talks with Saudi Foreign Minister Adel al-Jubeir on Saturday night.
Zarif said his priority for the meeting was to discuss the implementation of the July 14 agreement under which Iran agreed to take steps to curtail its nuclear programme in exchange for relief from economic sanctions that have crippled its economy.
"We hope that by its full implementation – its good-faith implementation – we can vent some of the mistrust that has existed over the past many decades," Zarif told reporters.
Iran is willing to discuss Syria with the United States, a senior Iranian official said.
"To help establishment of peace and security in the region, Iran is a key player. Therefore, we can offer our views and solutions to end crises in Syria and Yemen or any other regional issue," the Iranian official told Reuters.
Diplomats have said Iran might consider Assad's departure but suggested Tehran wants him to be succeeded by another Alawite government in Sunni-majority Syria, a stance that could be unacceptable to the United States, let alone Syrian Sunnis.
Robert Ford, a former U.S. ambassador to Syria, played down the chances of rapid progress, saying the big powers disagree on what is the main problem and how to address it.
"The Russians think the biggest problem is the Islamic State and the way to fix it is that people should stop fighting Bashar al-Assad and should help him," Ford said. "The American/Turkish/Saudi position is Bashar al-Assad is the biggest problem."
"This isn't going to be solved anytime soon," he added.
Kerry told Zarif of Washington's desire to see three U.S. citizens detained in Iran and a fourth who went missing there reunited with their families, the State Department said.
Jason Rezaian, Tehran bureau chief for the Washington Post,
was arrested in July 2014 and charged with espionage. Two other U.S. citizens are detained in Iran: Christian pastor Saeed Abedini and Amir Hekmati, a former U.S. Marine Corps sergeant.
Robert Levinson, a private investigator, disappeared in Iran in 2007.
(Additional Reporting by Lesley Wroughton; Editing by Louis Charbonneau and Sandra Maler)