Washington: The United States and Russia announced plans for a cessation of hostilities in Syria would take effect on Saturday but exclude militants from the IS militant group, Nusra Front and others the United Nations deems as terrorist groups.
Parties would indicate their agreement to the United States and Russia by noon on Friday Damascus time (1000GMT), and the truce would go into effect at midnight, the two countries said in a joint statement issued by the US State Department.
Under the terms of the deal, Syrian government and allied forces will cease attacks against armed opposition forces, and vice versa, with any weapons including rockets, mortars, anti-tank guided missiles.
However, the US-Russian plan leaves a loophole by allowing continued attacks, including air strikes, against IS, Nusra and other militants. Because of the mingling of forces, this could result in continued attacks against armed opposition members who are parties to the cessation of hostilities.
"Military actions, including air strikes, of the Armed Forces of the Syrian Arab Republic, the Russian Armed Forces, and the US-led Counter IS Coalition will continue against IS, 'Jabhat Al Nusra' (Nusra Front) and other terrorist organisations designated by the UN Security Council," the joint statement said.
It added that Russia, the United States and others would work together to delineate the territory held by IS, Nusra Front and other groups deemed terrorists by the UN Security Council which are excluded from the truce.
United Nations Secretary-General Ban Ki-moon welcomed the US-Russian announcement and called on all warring parties to implement it, Ban's spokesman said.
A cessation of hostilities is meant to be "a first step towards a more durable ceasefire," UN spokesman Stephane Dujarric told reporters about the agreement.
"The Secretary-General strongly urges the parties to abide by the terms of the agreement," he said. "Much work now lies ahead to ensure its implementation, and the international community, the ISSG (International Syria Support Group) and the Syrian parties must remain steadfast in their resolve."
Syrian National Coalition president Khaled Khoja, a member of the opposition High Negotiations Committee said the truce would be for an initial two weeks, with the possibility to extend it.
"The length of the proposed truce is two weeks, but it could be extended indefinitely if the parties commit to it," said Khoja,
Meanwhile, IS attacked the Syrian government's main supply route from Damascus to the northern Syrian city of Aleppo on Monday.
The Syrian Observatory for Human Rights said fighting and air strikes continue unabated across the country.
IS said it had taken control of a number of villages along an important road which connects government-held areas of Aleppo with the cities further south. A Syrian military source confirmed the attack but said it was repelled.
"They tried to attack this road, they were repelled and suffered big losses," the source said. "After their great losses, they are seeking any propaganda operation."
The Observatory's director, Rami Abdulrahman, said government forces had reclaimed one of four positions seized by IS on the road, which it has cut in previous attacks. "The regime has recovered one of four positions that IS took on the road," Abdulrahman said.
IS said it was responsible for multiple bomb blasts on Sunday in Sayeda Zeinab, a southern district of Damascus, which state media said killed 83 people and injured dozens. It also said it carried out twin car bomb blasts in Homs which state media said killed at least at least 39.
The Observatory put the death toll from these attacks higher, with at least 120 killed in Damascus and 64 in Homs.
A UN-backed panel said that war crimes in Syria's five-year-old conflict are widespread and Syrian government forces and IS militants continue to commit crimes against humanity in the face of inaction by the international community.
"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.
"The stipulations of relevant Security Council resolutions... remain largely unheeded and unimplemented," it said. "Crimes against humanity continue to be committed by government forces and by ISIS (Islamic State). War crimes are rampant."
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 commission's chairman, Paulo Pinheiro, told reporters at UN headquarters that no warring party respects international humanitarian law.
"The fractured Syrian State is on the brink of collapse," the commission said in its 31-page report. "Indiscriminate and disproportionate attacks on the civilian population must be brought to an end."
"Government forces, anti-government armed groups and terrorist organizations 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. Their suffering has been compounded by an absence of civilian protection," it added.