The latest push to bring at least a temporary halt to the fighting in Syria continues Monday with the United States and Russia trying to convince opposing sides of the conflict to accept a cease-fire proposal.
U.S. Secretary of State John Kerry said Sunday a "provisional agreement" had been reached with Russia and could begin within a few days.
Kerry spoke by telephone with Russian Foreign Minister Sergei Lavrov, whose ministry said the two powers agreed on the parameters of the cease-fire. Neither diplomat released details of the plan.
But even as talk again focused on stopping the fighting, violence continued Sunday with massive bomb attacks claimed by the Islamic State group in Damascus and Homs. The Damascus attacks killed at least 83 people, while another 59 died in Homs.
U.N. envoy for Syria Staffan de Mistura strongly condemned the bombings. Earlier this month, he suspended peace talks between the government and opposition groups with the hope of resuming them this week, but on Friday said that was no longer realistic.
WATCH: US Secretary of State Kerry discusses Syria conflict
Syrian President Bashar al-Assad said his government is ready for a cease-fire, but not if "terrorists" use it to bolster their positions. He has regularly referred to any opposition fighters as terrorists throughout the conflict that began in March 2011.
Kerry said Assad-ally Russia would be speaking with the Syrian government, as well as Iran, while the U.S. would be consulting with opposition groups in order to try to implement the cease-fire.
Rebel group 'willing'
The main rebel coalition in Syria has said it is willing to accept a temporary truce, but only if Russia calls a halt to its airstrikes and the Damascus government ends its offensive near the Syrian-Turkish border.
Russia has said it will not stop its airstrikes against what it calls terrorist targets in Syria, even if there is international agreement on a temporary truce, which diplomats have been calling a "cessation of hostilities."
The United States and others involved in trying to end the Syrian civil war say most Russian bombs are directed at rebels fighting the Syrian government, not at Islamic State terrorists.
U.S. officials have given a guarded account a conversation Kerry and Lavrov had Saturday, reviewing the work of two teams working in Geneva on the Syrian crisis – one on the urgent need to get humanitarian assistance to civilians trapped by the civil war in Syria, the other on a temporary truce intended to lead to a full and formal cease-fire.
Both sides agreed there has been some progress in delivering aid shipments to civilian neighborhoods under siege by Syrian government troops and their allies.
A U.S. statement added that humanitarian groups need immediate access to additional areas, and that future deliveries should be "sustained and unimpeded."
The Syrian rebel coalition known as the High Negotiations Committee met in Saudi Arabia Saturday and condemned Russia's military action supporting the Damascus government. The coalition said Russia has "shown disdain for the international community and disregard for the lives of Syrians."
Russia's airstrikes have been blamed for increasing the war's toll on Syrian civilians, prompting more of them to leave their homes as refugees and try to flee across the border into Turkey.
Russia's UN request rejected
Moscow has complained that Turkey is about to send ground forces into Syria, and it called for Security Council action to block that at an emergency meeting Friday.
Other Security Council members rejected Russia's draft resolution, and Turkey's U.N. ambassador said his country would only take such a direct role in Syria if it was backed by the United Nations.
Russia's proposal to the Security Council did not mention Turkey by name, but its intent was clear. It strongly condemned cross-border shelling into Syria and what Russia says is an unrestricted flow of "terrorist" fighters and illegal weapons shipments into the country.
Syria's main opposition group agreed to the "possibility" of a temporary truce Saturday while harshly criticizing Russia for failing to hold to a temporary agreed-upon cease-fire.
The High Negotiations Committee, a Saudi-backed coalition of Syrian opposition groups, issued a statement saying Russia had shown "disdain for the international community and disregard for the lives of Syrians." The groups agreed on the possibility of a deal if the United Nations could guarantee a cease-fire and the delivery of humanitarian aid.
The statement followed Russia's call for an urgent meeting of the U.N. Security Council to discuss its concerns that Turkey may be planning to send ground troops into Syria.
The Russian delegation presented a one-page draft resolution that would have condemned such a move. It also “strongly” condemned cross-border shelling, the flow of terrorist fighters and the illegal movement of weapons from Syria’s “neighbors.”