The United States, Russia and Jordan have reached a ceasefire and "de-escalation agreement" in southwestern Syria, one of the combat zones in a six-year-old civil war, Washington and Moscow said on Friday.
The ceasefire will go into effect at noon Damascus time (0900 GMT) on Sunday, U.S. and Russian officials said.
The deal was announced after a meeting between U.S. President Donald Trump and Russian President Vladimir Putin at the G-20 summit of major economies in the German city of Hamburg.
U.S. Secretary of State Rex Tillerson said the area covered by the ceasefire affects Jordan's security and is a "very complicated part of the Syrian battlefield." Russia and Iran are the main international backers of Syrian President Bashar al-Assad while Washington supports some of the rebel groups fighting to topple him.
"I think this is our first indication of the U.S. and Russia being able to work together in Syria, and as a result of that we had a very lengthy discussion regarding other areas in Syria that we can continue to work together on to de-escalate the areas," Tillerson said.
The conflict has killed nearly half a million people, according to the Britain-based Syrian Observatory for Human Rights, turned cities into ruins and forced millions to flee Syria.
Previous similar ceasefires have failed to hold for long.
Trump ordered missile strikes against a Syrian air base in April to punish Assad after a chemical weapons attack but this is the first time his administration has been so directly involved in a peace-making attempt there.
Backed by Russian air power, Assad has regained ground in the last year or so lost to the mostly Sunni Muslim rebels.
The Syria deal appeared to be the main point of agreement at the first meeting between Trump and Putin, who also discussed Moscow's alleged interference in the U.S. 2016 presidential election and North Korea's nuclear ambitions.
Goals in Syria
Lavrov said the accord includes "securing humanitarian access and setting up contacts between the opposition in the region and a monitoring center that is being established in Jordan's capital."
Tillerson said that by and large the objectives of the United States and Russia in Syria "are exactly the same."
But Washington and Moscow have long been at odds over Syria.
The United States has often called for the removal of Assad, who it blames for shootings of protesters at the start of the conflict and, more recently, chemical weapons attacks on civilians.
Russia and Iran strongly back the Syrian leader, who gives both countries a strategic foothold in the Mediterranean Sea.
Despite the ceasefire deal, Tillerson said the United States still sees "no long-term role for the Assad family or the Assad regime. And we have made this clear to everyone. We certainly made it clear in our discussions with Russia."
Robert Ford, who resigned in 2014 as U.S. ambassador to Syria over policy disagreements, said the Trump administration, like that of former President Barack Obama, has "no national objective for the future of Syria nor any strategy for how to secure an objective were one identified."
By contrast, Russia's overall aim is clearer, said Ford, now a fellow at the Middle East Institute think tank in Washington.
"The Russian objective is to insulate Damascus and the Syrian national government from outside pressure trying to pressure it into major concessions," he said.
A group of Syrian rebels that took part in the latest peace talks in Kazakhstan this month said in a statement it had "great concern over the secret meetings between Russia and Jordan and America to conclude an individual deal for southern Syria in isolation from the north," which it described as an unprecedented event that "divides Syria and the opposition."
The Syrian government and the Southern Front, the main grouping of Western-backed rebel groups in southwest Syria, did not immediately react to the ceasefire deal.
It was not immediately clear exactly which areas of southwestern Syria would be covered by the ceasefire but earlier talks between the United States and Russia about a "de-escalation zone" covered Deraa province, on the border with Jordan, and Quneitra, which borders the Israeli-occupied Golan Heights.
British Defense Secretary Michael Fallon welcomed any ceasefire in Syria but wanted to see results on the ground.
"The recent history of the Syrian civil war is littered with ceasefires and it would be nice ... one day to have a ceasefire," Fallon said at an event in Washington.