U.S. Secretary of State John Kerry said on Friday Washington and Moscow had reached a common understanding on the steps now needed to get Syria's peace process back on track.
But Kerry, after a day of talks in Moscow with his Russian counterpart, said more work was needed before those steps could be implemented, and that Russia and the United States still differed over the future of Syrian President Bashar al-Assad.
Five years into a Syrian civil war that has killed thousands and forced millions to flee their homes, Russia and the United States are the most influential outside players in the conflict, but the objectives they are pursuing diverge.
Russia backs Assad and is giving military help to his campaign against rebel fighters, while the United States believes the Syrian leader has to go and is supporting some of the rebel groups who are fighting to unseat him.
At a news conference alongside Russian Foreign Minister Sergei Lavrov, Kerry identified two problems that have damaged an internationally-brokered ceasefire in Syria: attacks carried out by the Nusra Front, al Qaeda's Syrian affiliate, and what Kerry described as indiscriminate bombing by Assad's forces.
"We have agreed to steps that if implemented in good faith can address two serious problems I have just described about the cessation," said Kerry.
"It is possible to help restore the cessation of hostilities, significantly reduce the violence and help create the space for a genuine and credible political transition."
"The concrete steps we have agreed on are not going to be laid out in public in some long list because we want them to work and because they need more work in order to work."
The Russian foreign minister also said he and Kerry had made progress over Syria, after talks that started on Friday morning and lasted deep into the night.
"We have a common understanding about these concrete steps, which Russia and the USA - as co-chairs of the Syria Support Group - could take to enhance the effectiveness of our work," Lavrov said.
Kerry has been accused by some within the U.S. foreign policy establishment of being too willing to make concessions to Russia over Syria. But he stressed that Washington's policy has not changed "one iota."
"We still believe that Syria can’t have peace while Assad is there. We have a difference with Russia on that," Kerry said.
Soon after flying in to Moscow late on Thursday, Kerry had talks with Russian President Vladimir Putin that focused on the conflict in Syria.
The Washington Post newspaper had reported that Kerry was bringing with him to Moscow a proposal for intelligence sharing with Russia over Syria and joint selection of bombing targets.
But a Kremlin spokesman said that Putin and Kerry had not directly discussed military cooperation between Moscow and Washington in Syria.
At the start of their talks on Friday morning, both Kerry and Lavrov said that the attacks in the French city of Nice underscored the need to join together in fighting terror.
Dozens of people were killed on Thursday when a gunman drove a heavy truck at high speed into a crowd in Nice who were celebrating Bastille Day, France's national holiday. French authorities said it was a terrorist attack.
Referring to what he described as the "incredible carnage" in Nice, Kerry said nowhere was there a greater hotbed for terrorists than in Syria. He said people all over the world were looking to world leaders to do everything possible to combat terrorism.
Kerry and Lavrov broke off their talks and took the short drive to the French embassy in Moscow, where they each laid a bouquet of flowers in remembrance of the victims in the Nice attack, and signed a book of condolences.