Could the nuclear deal with Iran help ease the way toward peace talks on ending Syria's civil war? Immediately after the accord with Iran was finalized, U.S. Secretary of State John Kerry and British Foreign Secretary William Hague set to work to prepare a political transition to stop the fighting in Syria.
Iran is the principal backer of Syrian military strikes against government opponents and has made clear its intention to carry that influence to planned peace talks in Geneva.
Iran's Deputy Foreign Minister Hossein Amir-Abdollahian says there is no excluding Tehran.
"Without any doubt, the Islamic Republic of Iran will play an active and constructive role in the political settlement of the Syrian problem," said Amir-Abdollahian.
So how does this weekend's deal to limit Iran's nuclear program affect its willingness to cooperate on Syria? Secretary Kerry said Iran choosing to "rejoin the community of nations" is an important first step toward playing a more constructive role in the region.
"It is fair to say that Iran’s choices have created a very significant barrier, and huge security concerns for our friends in the region, for Israel, for Gulf states and others, and obviously they have made certain choices that are deeply, profoundly unsettling in terms of stability in the region," said Kerry.
Tehran's support for Bashar al-Assad's military helps maintain its regional influence and resupply the Lebanon-based Islamic military group Hezbollah, while keeping its predominantly-Sunni Islam enemies off-balance, according to former U.S. ambassador Adam Ereli.
"Iran supporting Bashar al-Assad is as critical to the survival of the regime as developing a nuclear weapon," said Ereli.
From Geneva, Kerry came to London for talks with Hague on how Assad opponents might help form a transitional government.
While the main opposition coalition says it will take part in those talks, it is rejecting any further role for President Assad. Provisional opposition deputy prime minister Aiad Koudsi thinks talking with the regime is unlikely to produce any positive results.
"Sitting and negotiating with the Syrian regime is kind of like a useless process, a useless exercise. It is an exercise of futility that you cannot get anything out of it," said Koudsi.
That is a deal-breaker for the government in Damascus, which says it will not come to talks meant to topple the president. American University professor Akbar Ahmed thinks the Assad administration could provide an element of stability and prevent an all-out sectarian war from developing.
"You can see the tensions in a country like Syria, tensions which are contained by a strong man, a dictator. And when that dictator loosens his grip, as we saw with Iraq, suddenly all hell breaks loose," said Ahmed.
U.S. and Russian officials meeting Monday in Geneva to prepare for those talks are also working to address the war's humanitarian costs, including the needs of more than two million refugees who have fled from the fighting.