Russia and the US have agreed to coordinate air strikes against Islamist militants in Syria, part of a detailed agreement to reduce the violence there.
The plan will begin with a "cessation of hostilities" from sunset on Monday. Syrian forces will end combat missions in specified opposition-held areas.
Russia and the US will then establish a joint centre to combat jihadist groups, including so-called Islamic State (IS).
A Syrian opposition coalition has cautiously welcomed the agreement.
"We hope this will be the beginning of the end of the civilians' ordeal," said Bassma Kodmani, a spokeswoman for the High Negotiations Committee.
"We welcome the deal if it is going to be enforced."
In other reaction:
- Turkey welcomed the plan, and said aid needed to reach those in need "from the first day"
- EU foreign policy chief Federica Mogherini urged the UN to "prepare a proposal for political transition" in Syria
- British Foreign Secretary Boris Johnson urged Russia to "use all its influence" to ensure the Syrian government "delivers on its obligations"
Aid access
The announcement follows talks in Geneva between US Secretary of State John Kerry and his Russian counterpart, Sergei Lavrov.
The plan would need both the regime and opposition "to meet their obligations", Mr Kerry said.
The opposition had indicated it was prepared to comply with the plan, he said, provided the Syrian government "shows it is serious".
Mr Lavrov said Russia had informed the Syrian government about the arrangements and the Syrian government was "ready to fulfil them".
The accord also provides for humanitarian access.
"The cessation of hostilities requires access to all besieged and hard-to-reach areas, including Aleppo," Mr Kerry said.
Seven days after the start of the cessation of hostilities, Russia and the US will establish a "joint implementation centre" to fight IS and another main group, Jabhat Fateh al-Sham.
Jabhat Fateh al-Sham used to be known as the Nusra Front but changed its name in June and announced it was cutting ties with al-Qaeda.
Mr Lavrov said the joint implementation centre would allow Russian and US forces to "separate the terrorists from the moderate opposition".
He said the Russian and US air forces would carry out co-ordinated strikes against the two groups, and that in some areas, that excluded action by the Syrian air force.
"We have agreed on the areas where such co-ordinated strikes would be taking place, and in those areas, on neutral agreement shared by the Syrian government as well, only the Russian and US air force will be functional," he said.
But Mr Lavrov added that "the Syrian air force will be functional in other areas, outside those that we have singled out for Russian-American military co-operation".