Moscow (AFP) - US Secretary of State John Kerry and Russian counterpart Sergei Lavrov said Friday they had agreed on "concrete steps" to salvage a failing truce and tackle jihadist groups in Syria but refrained from laying out their deal.
The top diplomats emerged from 12-hour marathon talks saying they agreed on the way forward, but Kerry stressed that the details of the deal would not be made public to allow the "quiet business" of peacemaking to continue.
"I want to emphasise though that they are not based on trust, they define specific sequential responsibilities all parties to the conflict must assume with the intent to stop altogether the indiscriminate bombing of the Assad regime and stepping up our efforts against Al-Nusra," Kerry said, referring to the Syrian branch of Al-Qaeda.
"Each of us know exactly what we have to do."
Speaking alongside Lavrov, Kerry told reporters that if the steps are implemented "in good faith", they could "help restore the cessation of hostilities, significantly reduce the violence and help create the space for a negotiated and credible political transition."
The United States was touting a proposal for closer US-Russian military cooperation in Syria against Al-Qaeda and Islamic State fighters, but Russia has been cool to the idea.
In exchange, Moscow would be required to pressure its ally Syrian strongman Bashar al-Assad to ground his own jets and end attacks on civilians and the moderate opposition.
Earlier in the day, Kerry and Lavrov paid tribute to the victims of the Nice truck attack that has left at least 84 people dead by laying flowers in front of the French embassy in Moscow and signing a book of condolences.
They had also begun their talks Friday morning with a minute's silence for the victims of what US President Barack Obama described as a "tragic and appalling" attack, with Kerry stressing the importance of a united front against extremism.
- Time running out -
US officials were careful not to call the talks a last chance for diplomacy to resolve the bloody five-year-old conflict, but they warned time was running out.
Washington blames the failure of the peace process on Assad's ceasefire violations and on Al-Nusra's increasing influence among the surviving rebel factions.
"If we cannot get to a solution that resolves both of those problems we're going to be in a very different place, and the reality is that time is short here," a US official said.
Meanwhile, there was no sign in Damascus that Assad feels under any pressure to agree to talks on a new government, the next stage in the process if a ceasefire is restored.
Speaking to NBC News in Damascus, in an interview broadcast Thursday, Assad insisted Putin and Lavrov had never raised the issue of his departure.
"Only the Syrian people define who's going to be the president, when to come, and when to go. They never said a single word regarding this," he said.
Moscow and Washington and the 22-member contact group they co-chair have called for a nationwide ceasefire and Geneva-based talks on a "political transition".
A landmark partial ceasefire they brokered in February -- which did not include Islamic State or Al-Nusra -- has since all but collapsed amid continued heavy fighting.
UN Syria envoy Staffan de Mistura urged Russia and the United States to push for a resumption of the talks next month.
Lavrov meanwhile said the two sides were in favour of seeing the UN envoy "step up his work and make concrete proposals on the political transition and political reforms for all Syrian parties (in the conflict)".
Russian forces are fighting in support of Assad's regime against a variety of rebel factions while a US-led coalition focuses its fire on the Islamic State group.
Syria's civil war erupted in 2011 when Assad brutally suppressed anti-government demonstrations and has evolved into catastrophe that has left more than 280,000 dead.
Efforts to end the war have taken on greater urgency since the emergence of the Islamic State jihadist group, which seized control of large parts of Syria and Iraq in 2014.