The United States and Russia on Monday announced plans for a cessation of hostilities in Syria, excluding ISIL and Jabhat Al Nusra militants, that would take effect starting on Saturday.The warring factions would indicate their agreement by midday on Friday Damascus time, and the cessation of hostilities would go into effect at midnight, the two nations said in a joint statement issued by the US state department.A member of the Syrian opposition High Negotiations Committee said the truce would be for an initial two weeks, with the possibility to extend it.“It could be extended indefinitely if the parties commit to it,” said Khaled Khoja, president of the Syrian National Coalition.The Saudi-backed HNC, which comprises both political and armed opposition groups, met in Riyadh to discuss the US-Russian plan for a truce, which was announced by the US secretary of state John Kerry in Amman on Sunday.UN spokesman Stephane Dujarric said the cessation of hostilities was meant to be “a first step towards a more durable ceasefire”.The Russian foreign ministry said earlier on Monday that foreign minister Sergei Lavrov and Kerry spoke twice by telephone on Sunday and agreed on the parameters for the ceasefire, which were then reported to Mr Putin and Mr Obama.The HNC has said any ceasefire must include provisions for Russia, Iran and foreign militia forces backing the Syrian regime to stop fighting.Russia launched air strikes in Syria in September against what it said were “terrorists”, but has been accused of bombing moderate rebel forces in support of President Bashar Al Assad, a longtime ally.Iran has sent military advisers to Syria and the Tehran-backed Lebanese Shiite movement Hizbollah has deployed at least 6,000 militants to fight for Al Assad.Iran would have to be on board for any ceasefire to work and Russian defence minister Sergei Shoigu made a surprise visit to Tehran on Sunday, saying he was delivering a “special message” from Putin to Iranian president Hassan Rouhani.It is hoped that a truce would allow for a resumption of peace talks in Geneva, which collapsed last month after the Syrian government launched a massive offensive backed by Russian air strikes in the northern province of Aleppo. A truce would also allow for delivery of humanitarian aid to citizens trapped in besieged areas of the country. World powers under the aegis of the International Syria Support Group earlier this month announced a plan for a temporary truce that was to have taken effect from Friday. Instead, fighting intensified with Syrian regime forces pressing their offensive and Turkey shelling a Syrian Kurd-led alliance that is backed by the US as an effective ground force against the extremist group ISIL.Underlining the urgent need for a truce, a UN-backed panel on Monday said that war crimes in Syria’s five-year-old conflict were widespread and that government forces and ISIL militants continue to commit crimes against humanity.“Flagrant violations of human rights and international humanitarian law continue unabated, aggravated by blatant impunity,” the UN Independent International Commission of Inquiry said in its latest report.“Government forces, anti-government armed groups and terrorist organisations employ sieges and consequent starvation, denial of humanitarian access and other forms of deprivation as instruments of war to force surrender or to extract political concessions,” it said.“Civilians, who bear the brunt, serve as little more than pawns.” The UN inquiry, composed of independent experts, has long denounced the use of starvation by both sides in the Syrian conflict as a weapon of war, and has a confidential list of suspected war criminals and military units from all sides which is kept in a UN safe in Geneva.“The fractured Syrian state is on the brink of collapse,” the commission said. “Indiscriminate and disproportionate attacks on the civilian population must be brought to an end.”