A nationwide truce in Syria effective from sundown on Monday, improved humanitarian aid access and joint military targeting of banned Islamist groups are part of a peace deal brokered by the US and Russia being hailed as a breakthrough.
"Today Sergei Lavrov and I, on behalf of our presidents and our countries, call on every Syrian stakeholder to support the plan that the United States and Russia have reached, to... bring this catastrophic conflict to the quickest possible end through a political process," US Secretary of State John Kerry told a news conference on Saturday after marathon talks in the Swiss city.
Russian Foreign Minister Sergei Lavrov said that despite continuing mistrust, the two sides had developed five documents that would revive a failed truce agreed in February and enable military co-ordination between the US and Russia against militant groups in Syria.
Both sides agreed not to release the documents publicly.
"This all creates the necessary conditions for resumption of the political process, which has been stalling for a long time," Lavrov told a news conference.
The deal followed talks that stretched late into Friday night and several failed attempts to hammer out a deal over the past two weeks. The announcement on Friday was delayed as Kerry and US negotiators consulted officials in Washington.
Kerry said the "bedrock" of the new deal was an agreement that the government of Syrian President Bashar al-Assad would not fly combat missions in an agreed area on the pretext of hunting fighters from the banned Nusra Front, an al-Qaida affiliate in Syria.
"That should put an end to the barrel bombs, and an end to the indiscriminate bombing, and it has the potential to change the nature of the conflict."
Under the agreement, Russian-backed government forces and opposition groups, supported by the United States and Gulf States, would halt fighting for a while as a confidence-building measure. During that time, opposition fighters would have the chance to separate from militant groups in areas, such as Aleppo, where they had intermingled.
If the truce holds from Monday, Russia and the United States will begin seven days of preparatory work to set up a "joint implementation centre", where they will share information to delineate territory controlled by Nusra and opposition groups.
Both warring sides would pull back from the strategic Castello Road in Aleppo to create a demilitarised zone, while opposition and government groups would have to provide safe and unhindered access via Ramouseh in the south of the city.
"We must go after these terrorists," Kerry said. "Not indiscriminately, but in a strategic, precise and judicious manner so they cannot continue to use the regime's indiscriminate bombing to rally people to their hateful crimes."
Kerry cautioned opposition fighters that if they did not separate from Nusra they would not be spared from air attacks.
"This requires halting all attacks, including aerial bombardments, and any attempts to gain additional territory at the expense of the parties to the cessation. It requires unimpeded and sustained humanitarian access to all of the besieged and hard-to-reach areas including Aleppo."
The Pentagon said it would carefully monitor the "preliminary understanding" agreed on Friday.
The UN special envoy for Syria, Staffan de Mistura, welcomed the announcement, saying it had provided "clear rules" for a cessation of hostilities and would allow warring sides to resume political talks on a transition.