The United Nations special envoy for Syria said Friday he plans to resume peace talks on March 7 if a "cessation of hostilities" - due to start at 2200 GMT - negotiated by the United States and Russia and set to begin at midnight local time "largely holds."Staffan de Mistura briefed the U.N. Security Council via videoconference from Geneva following a meeting of envoys from the 17-member International Syria Support Group, which is supposed to monitor implementation of the agreement.De Mistura said he has "no doubt there will be no shortage of attempts to undermine this process.""This will remain a complicated, painstaking process," he told the council. But he added that "nothing is impossible, especially at this moment."De Mistura had abruptly aborted a first round of talks on Feb. 3 and urged countries in the International Syria Support Group (ISSG), led by the United States and Russia, to do more preparatory work.Shortly after de Mistura's briefing, the 15-member council voted unanimously to approve a resolution endorsing the cease-fire agreement.If the cessation of hostilities holds, it would mark the first time international negotiations have managed to achieve a pause in Syria's civil war, which shortly will enter its sixth year.According to a draft obtained by The Associated Press, the resolution urges the U.N. secretary-general to resume the peace talks "as soon as possible."It also expresses support for an international working group whose task is to "accelerate the urgent delivery of humanitarian aid," with the goal of sustained and unimpeded aid access to all parts of Syria.That includes areas where hundreds of thousands of people find themselves besieged, most of them by Syrian government forces or Daesh.For the cease-fire to succeed, multiple armed factions will have to adhere to its terms.The Syrian government and a leading opposition bloc have agreed to the cessation of hostilities, but the accord excludes U.N.-designated terrorist groups like Daesh and Nusra Front, which hold swaths of Syrian territory.U.S. Ambassador Samantha Power told the council that the cessation of hostilities will not in itself ensure that a political solution in Syria is reached. But she said the "vast majority" of the opposition is ready to cooperate with the cease-fire."Let us be real. It's going to be extremely challenging, especially at the outset, to make this work," Power said.In Washington, U.S. State Department Mark Toner expressed confidence in the cessation of hostilities, pointing out that the opposition's High Negotiations Committee and Syrian Democratic Forces, and the vast majority of its armed groups, have accepted the terms."The Russians have committed themselves to not carrying out strikes against groups that we consider the moderate opposition," Toner told reporters.But he called it "put up or shut up" time for Russia to prove its seriousness about ending the fighting and starting a political transition.Russia sounded a positive note at the Security Council meeting."We now have a real chance to end the violence," said Russian deputy foreign minister Gennady Gatilov, who acknowledged that the process will be "difficult and complex."But warplanes on Friday continued to launch airstrikes against rebel-held positions in the suburbs of the Syrian capital and near the northern city of Aleppo. A spokesman for the U.N. secretary-general acknowledged "an increase of military activity across the board in Syria" in the hours leading up to the cease-fire."It's tragic but unfortunately not surprising," Stephane Dujarric said, adding: "The only thing that is required is for people to take their fingers off the trigger."