After a meeting with diplomats Thursday evening in Munich, U.S. Secretary of State John Kerry said Syria will implement a "nationwide cessation of hostilities" within one week.
World leaders, including the U.S., Russia, Saudi Arabia and Iran, were meeting in Munich with the aim of restarting the peace talks between the government and Syrian opposition.
Kerry said after the meeting that the target is to begin a cease-fire in Syria's civil war in a week's time. He said that would not apply to the Islamic State in Iraq and the Levant or Jabhat Al-Nusra.
Kerry said diplomats from the U.S., Russia and other powers also agreed to "accelerate and expand" the delivery of humanitarian aid immediately, bringing aid to besieged areas.
A working group is to start meeting in Geneva Immediately to oversee that.
Russian Foreign Minister Sergey Lavrov said that peace talks should resume in Geneva as soon as possible, and that all opposition groups should participate.
Speaking after marathon talks that included more than a dozen other countries, Lavrov also said that halting hostilities in Syria would be a difficult task.
Despite the difficulty, and a series of previous failed cease-fires, major powers agreed on Friday to the plan aimed at breaking the deadlock in Syria. Kerry said that a long-term cease-fire in Syria depends on parties to its civil war engaging in "genuine negotiation."
Kerry, flanked by Lavrov and U.N. envoy Staffan de Mistura, acknowledged that the Munich meeting produced commitments on paper only. He and Lavrov agreed that the "real test" will be whether all parties to the Syrian conflict honor those commitments.
Kerry said that "the objective is to achieve a durable long-term cease-fire at some point in time" but that depends on future negotiations. The U.S. secretary of state acknowledged that differences remain over the future of Syrian President Bashar al-Assad but said "you have to be at the table to deal with that."
The peace talks took place against the backdrop of the fierce fight for control of Syria's Aleppo province, which continued unabated.
The Syrian government, backed by Russian air strikes, launched a major offensive from the north of Aleppo and captured several strategically important towns earlier this month.
The offensive has led to the displacement of more than 50,000 civilians from Aleppo, tens of thousands of whom have amassed in camps at the Turkish border.
March would make the fifth anniversary of the start of Syria's war — which has killed nearly half a million people and contributed to a major refugee crisis in the Middle East and Europe as residents fled the carnage.
The fighting has left much of the country in ruins, with major cities such as Homs and Aleppo almost completely destroyed.
Al Jazeera and wire services