US Secretary of State John Kerry said that Washington and Moscow had agreed on "concrete steps" to save the failing Syrian ceasefire.
But, appearing with Russia's Foreign Minister Sergei Lavrov, he yesterday said 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."
Kerry added that if the steps were 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".
Kerry's 12-hour marathon talks with Lavrov came after what the top US diplomat said were "serious and frank" talks with Russian President Vladimir Putin on Thursday.
According to a leaked document seen by the Washington Post, Kerry was set to push for Moscow to more closely cooperate with the US military against the Al-Nusra Front jihadist group in Syria.
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.
Lavrov meanwhile said the two sides were in favour of seeing UN Syria envoy Staffan de Mistura "step up his work and make concrete proposals on the political transition and political reforms for all Syrian parties (in the conflict)".
UN Syria envoy Staffan de Mistura had urged Moscow and Washington to push for a resumption of the talks next month.
De Mistura said peace talks "have a target date of August" and need to be "a credible beginning of a roadmap towards a political transition".
The diplomatic push comes as ferocious bloodshed in Syria continues following a series of failed ceasefires and one day after at least 84 people were killed in Nice in what French authorities said was a "terrorist" attack.
