HANGZHOU, China (AP) -- The United States is skeptical an agreement with Russia to decease violence in Syria can work but will keep pursuing it nonetheless, President Barack Obama said Sunday as negotiators from both countries edged toward a deal.
Obama, speaking on the sidelines of the Group of 20 economic summit in China, said the U.S. and Russia still have "grave differences" about what's needed to end Syria's civil war and which opposition groups are legitimate targets for the U.S. and Russian militaries. But he said "it is worth trying" to secure an agreement nonetheless, adding that negotiators were working "around the clock."
"We're not there yet," Obama said. "I think it's premature for us to say there's a clear path forward, but there's the possibility at least for us to make some progress."
A deal could be announced as early as Sunday by U.S. Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov, said a senior U.S. State Department official, adding that the two countries were close to a deal but still had to resolve some issues. The official wasn't authorized to discuss the negotiations publicly and requested anonymity.
Kerry and Lavrov have been deep in talks for weeks over a deal to boost U.S. and Russian military cooperation to fight the Islamic State group and other extremists in Syria - a step Moscow has long sought. The emerging deal is expected to also include provisions to ensure aid can reach besieged areas of Syria and steps to prevent Syrian President Bashar Assad's government from bombing areas where U.S.-backed rebels are operating.
U.S. officials have said that as part of a deal, Russia would have to halt offensives by Assad's government, something it has failed to do over months of diplomatic efforts. They said the U.S. must get rebels to break ranks with the al-Qaida-linked Nusra Front, a task that grew tougher after Nusra fighters last month successfully broke the siege of Aleppo, Syria's largest city and the site of fierce recent fighting.
Though negotiators have been hopeful a deal could come together while world leaders are gathered in Hangzhou for the G20, that optimism has been tempered by the failure of previous ceasefire deals to hold. The U.S. has long been wary of increasing military coordination with Russia in Syria's civil war because it says Russia continues striking moderate, U.S.-backed opposition groups in a bid to prop up Assad. The U.S. wants Russia to focus exclusively on IS and al-Qaida-linked groups.
"These are difficult negotiations," Obama said. He added later: "If we do not get some buy-in from the Russians on reducing the violence and easing the humanitarian crisis, then it's difficult to see how we get to the next phase."
Discussions about the intractable Syria conflict and the related fight against IS have been a major focus as world leaders gather for the G20, which brings together the world's major economies. Obama, who met first Sunday with new British Prime Minister Theresa May, also planned to discuss Syria when he meets with Turkish President Recep Tayyip Erdogan, their first sit-down since the summer's failed coup in Turkey.
The attempted overthrow in Turkey has accelerated the deterioration in the relationship between Turkey and the United States. It led to Turkish accusations of U.S. involvement, and those tensions have been aggravated by growing clashes between Turkish forces and U.S.-backed Syrian Kurds.
The U.S., meanwhile, has expressed concern about Turkey's recent operations across its border into Syria. The Pentagon has backed the incursions, but said they should only be aimed at IS fighters. Turkey has used the operations to push back Syrian Kurds it accuses of seeking to claim more territory.
For the U.S., the dispute is a reminder of its increasing entanglement in the long-standing local rivalries and conflicts exposed by Syria's civil war.
Since the failed coup, the U.S. has been alarmed by Turkey's diplomatic flirtations with Russia, Syrian President Bashar Assad's patron, and apparent softening of its tone about the need for Assad to be excluded from a political transition. At the same time, the U.S. continues to work toward an agreement with Russia to cooperate more closely in the fight against IS in Syria.
In his first meeting with May since she took office in Britain, Obama sought to demonstrate American solidarity with the U.K. amid the tumult over its decision to leave the European Union. He and May both said their countries would continue an ambitious trade agenda together, though Obama conceded that Britain's first task was to figure out its new trade relationship with its EU neighbors.
Obama's previous suggestions that the U.S. would prioritize ongoing U.S.-EU trade talks over a one-on-one deal with Britain rankled London, but Obama said it was never intended to be a punishment.
"The bottom line is we don't have a stronger partner in the world than the United Kingdom," Obama said. "And despite the turbulence of the political events over the last several months, we have every intention of making sure that continues."
May, echoing Obama's commitment to continue close cooperation with the U.S. on economic and security issues, sought to put to bed any notion that the U.K. would hold another referendum or reverse course on the EU exit, or Brexit.
"The U.K. will indeed be leaving the European Union," she said.
Associated Press writer Bradley Klapper in Washington contributed to this report.