Top US diplomat John Kerry stressed the urgency of closer cooperation in Syria after the Kremlin said Friday a US proposal for direct military cooperation in the war-torn country had not been addressed in earlier talks with President Vladimir Putin.
On the second and final day of his visit to Moscow, Kerry called for stepping up cooperation between the United States and Russia to thwart jihadist groups and revive the stalled Syria peace process, hours after at least 84 people were killed in an attack in Nice.
"Nowhere is there a greater hotbed and incubator for these terrorists than in Syria," Kerry said after observing a minute of silence in honour of the victims ahead of his talks with Russian counterpart Sergei Lavrov.
"And I think people all over the world are looking to us and waiting for us to find a faster and more tangible way" to fight terrorism, Kerry said.
"And you and I and your teams are in the enviable position of actually being able to do something about it," he added, addressing Lavrov.
Kerry's meeting with Lavrov follows what the top US diplomat said were "serious and frank" talks with President Vladimir Putin on Thursday.
But the Kremlin said Friday that direct military cooperation between Moscow and Washington in Syria, a proposal Kerry was set to make, had not been addressed in Thursday's talks.
According to a leaked document seen by the Washington Post, Kerry's key proposal is to offer Russia closer US military cooperation against the Al-Nusra Front jihadist group.
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.
Kremlin spokesman Dmitry Peskov said Friday that the talks between Putin and Kerry had not marked the start of cooperation "to significantly improve the effectiveness of efforts in the fight against terrorism."
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 is 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 or a political transition.
"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-nation 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.
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 mid-2014.