MUNICH/DAMASCUS — World powers began work Friday on the details of a temporary truce in war-ravaged Syria, but rebels and aid groups on the ground were skeptical that the "ambitious" deal could be implemented.
The agreement, which followed talks between the U.S., Russia and more than a dozen other countries, calls for a "cessation of hostilities" within one week and the immediate expansion of humanitarian supplies.
Secretary of State John Kerry hailed the results but noted they were "commitments on paper," adding, "the real test is whether or not all the parties honor those commitments and implement them in reality."
Opposition groups gave a cautious welcome, but said there must be differences on the ground before they could work towards a permanent peace deal in Geneva.
Issam al-Reis, spokesman for the Free Syrian Army's southern front, called for "concerted international pressure on Russia" to adhere to the terms.
"We have no faith in words any longer, it's only concrete action that will make a difference to Syrians' lives at this dark time," he said in a statement. "There have been too many unimplemented empty statements."
In Damascus, opinions were split Friday between optimism and skepticism over whether there would actually be an end to the fighting.
Assad's picture is visible all over the city, and locals questioned whether he would pause the fighting at a time when his forces appear to have the upper hand.
NATO said it would step up monitoring along the Turkish border to oversee the implementation of the deal. "We have seen before that ceasefires are not always respected," Secretary-General Jens Stoltenberg told reporters.
Jean-Marie Guéhenno, president of the International Crisis Group, said he is "deeply skeptical" of the possibility of an end to violence in Syria, and that any progress is dependent on the groups on the ground.
"It might turn out to be more of a pause in fighting rather than a permanent ceasefire," he said.
Germany's defense minister, Ursula von der Leyen, said the deal "gave a spark of hope" but admitted it would only succeed if it was "fulfilled in the streets of Aleppo."
One major practical complication is that Friday's truce does not apply to U.N.-designated terror groups including ISIS or the al-Nusra Front. The U.S. and Russia are among the countries conducting air campaigns against ISIS in Syria.
Britain warned that no cease-fire could succeed unless Russia stopped air strikes on opposition groups in support of Syria's President Bashar Assad. Russia insists it is only targeting ISIS.
"Russia … claims to be attacking terrorist groups and yet consistently bombs non-extremist groups including civilians," U.K. foreign secretary, Philip Hammond, said in a statement. "If implemented fully and properly, this [deal] will be an important step toward relieving the killing and suffering in Syria. But it will only succeed if there is a major change of behavior by the Syrian regime and its supporters."
Aid groups also gave a qualified response, welcoming the temporary deal but underscoring the urgency of the humanitarian crisis.
"Why wait one more week before the fighting stops?" asked Neal Keny-Guyer, chief executive of Mercy Corps.
Greg Barrow, British head of the U.N. World Food Program, said: "If the checkpoints disappear, the aid trucks can roll in with supplies to these besieged communities - that's what we need to see."
ussia had proposed a March 1 cease-fire date, which the U.S. and others saw as a ploy to give Moscow and the Syrian army three more weeks to try to crush Western- and Arab-backed rebels. The U.S. countered with demands for an immediate stop to the fighting
Further talks in Munich were expected on Friday to discuss how aid deliveries could be made to affected areas and to mark out territories held by the ISIS and al-Nusra so that parties can comply with the deal.
The death toll in the five-year conflict is estimated at more than 250,000, and more than 4.5 million have fled the country, according to the United Nations.
—NBC News' Carlo Angerer and Kier Simmons contributed reporting.
This story originally appeared on NBCNews.com