The United States and Russia early Saturday announced an agreement on a plan to reduce violence in Syria, calling for a ceasefire starting at sundown on Monday and a move towards a political transition.
US Secretary of State John Kerry, speaking after more than 12 hours of consultations with Russian Foreign Minister Sergei Lavrov, said the deal could provide a "turning point" in the conflict if the parties implement it "in good faith."
"Working together, Russia and the United States and our teams, have devised what we think is a more prescriptive and far-reaching approach than we have been able to put together to date," Kerry said.
The plan would ensure that the Russian-backed Syrian government does not fly combat missions over rebel-held areas, which would allow humanitarian aid to reach people in need.
With Syrian government airstrikes halted, there's a potential to "change the nature of the conflict," Kerry said, noting that the strikes have been the main driver of casualties and migration flows.
The US and Russia also agreed on specific areas where the two countries will fight together against Islamic State extremists, Lavrov said.
He also said Russia had spoken to the Syrian government which had given its support for the agreement.
A spokesman for the High Negotiations Committee, a Syrian rebel umbrella group, told Russian news agency Tass that it would support the agreement if Syrian regime troops also respected the ceasefire.
UN envoy for Syria Staffan de Mistura welcomed the agreement and said he hoped the deal would help "renewed efforts to reach aSyrian-owned and Syrian-led political settlement of the conflict."
All sides will need to adhere to the cessation of hostilities for seven days before the plan can fully go into effect. Preparatory work to delineate areas held by the government, rebels and terrorists will also commence on Monday.
Kerry stressed that the US and Russia will carry out joint military strikes against terrorists only if there's a sustained period of reduced violence.
The meeting between the top US and Russian diplomats in Geneva had focused on achieving a durable ceasefire and stepping up humanitarian aid, according to the White House and diplomatic sources.
The US supports the opposition that is fighting to oust Syrian President Bashar al-Assad, an ally of Russia.
In February, after nearly five years of conflict, the US and Russia brokered a nationwide ceasefire in Syria.
It held for a time but then collapsed under the pressure of localized fighting and a failed UN-backed political process to end the violence.
There have been attempts since to reach short-term, often region-specific, cessations of hostilities, but these have tended to be short-lived.
Russia has emphasized the possibility of reaching a deal with Washington on military collaboration against terrorist groups in the country.
Russia's Foreign Ministry said Kerry and Lavrov discussed the possibility during a phone call on Thursday.
The conflict in Syria has intensified in recent months, worsening the humanitarian situation in the country.
Al-Assad’s forces and allied paramilitaries this week regained territory from rebels in the divided northern city of Aleppo.
The advance has allowed regime forces to impose a siege on Aleppo’s eastern rebel-held section, putting the fate of an estimated 250,000 to 300,000 residents there in jeopardy.
A UN humanitarian official warned on Friday that the situation in eastern Aleppo was “extremely severe.”
"Therefore, we continue to demand a 48-hour weekly humanitarian pause to reach the people in need," the UN's humanitarian affairs chief, Stephen O'Brien, said in Geneva.
Once Syria’s commercial hub, Aleppo has been divided between al-Assad's forces in the west and rebels to the east since fighting for control of the city erupted in mid-2012.