The United States and Russia have agreed a ceasefire in Syria that would take effect this weekend in an attempt to end five years of war in the country.
In a statement, the countries said the "cessation of hostilities" would begin on 27 February if opposition groups in Syria agree to the deal.
What does this mean?
Subject to agreement from Syrian opposition forces, a ceasefire would take effect this weekend with the US and Russia acting as enforcers and monitors of the "cessation of hostilities".
The agreement does not cover the co-called Islamic group or but would exclude the Islamic State and al-Nusra militants, both designated as terrorist organisations by the UN, to allow counter-terrorism operations to continue.
What has the US said?
Obama welcomed the agreement in the call with Putin that the White House said was arranged at the Russian's request. The White House said Obama emphasized the key is to ensure that Syria's government and opposition groups faithfully implement the deal.
White House spokesman Josh Earnest said it would "be difficult to implement."
"We know there are a lot of obstacles, and there are sure to be some setbacks."
US Secretary of State John Kerry welcomed the deal, saying: "If implemented and adhered to, this cessation will not only lead to a decline in violence, but also continue to expand the delivery of urgently needed humanitarian supplies to besieged areas."
What did President Putin say?
Russian President Vladimir Putin said the agreement was a real step towards halting the bloodshed and was an example of action against terrorism.
"I'm convinced that the joint actions agreed with the American side are able to radically transform the crisis situation in Syria," he said in a special address broadcast on the Kremlin's website.
Putin added that Russian and US negotiators had held several rounds of closed consultations, which had achieved "an important, definite result".
He said it was important that Russia and the U.S. "are able to launch an effective mechanism for realisation and monitoring of the ceasefire regime".
A "hot line" would be created to ensure ceasefire violations could be reported.
"The main thing is that conditions have been created for launching a genuine political process through the wide inter-Syrian dialogue in Geneva overseen by the UN," Putin said.
How has the news been received elsewhere?
The move was welcomed by UN Secretary-General Ban Ki Moon who called it "a first step towards a more durable ceasefire."
A spokeman for the UN told reporters: "The Secretary-General strongly urges the parties to abide by the terms of the agreement. Much work now lies ahead to ensure its implementation, and the international community and the Syrian parties must remain steadfast in their resolve."
The UN special envoy to Syria said the agreement would mean a speedy return to negotiations to secure a political solution to the conflict.
Turkey also welcomed the news, but urged Russia to restrain from attacks that might harm civilians.
"We hope that Russia, in its fight against Islamic State, will not fly its jets and kill innocent people," Deputy Prime Minister Numan Kurtulmus said.
ITV News' Washington Correspondent Robert Moore says: