US Secretary of State John Kerry has appealed to both sides to continue Syrian peace talks in Geneva despite an attack by Islamic State bombers that killed more than 60 people near the country's holiest Shi'ite shrine.
Kerry said on Sunday (local time) that the conflict could easily engulf the Middle East if no negotiated settlement was achieved.
He also called for immediate steps by all the parties to increase food aid and other humanitarian assistance to 13.5 million Syrians, including six million children.
"In the end there is no military solution to the conflict," Kerry said in a televised statement.
Kerry's statement came after a senior negotiator for the Syrian opposition delegation threatened to walk out of the talks if Syrian President Bashar al-Assad's forces and allies continued to escalate a bombing campaign in rebel-held areas and hamper delivery of humanitarian aid.
Since the beginning of 2015, the Syrian government approved only 13 of 113 requests made by the United Nations to deliver humanitarian aid, Kerry said. And only one in 100 Syrians had received any food aid at all in 2015.
"Let me be clear: The Syrian regime has a fundamental responsibility -- all the parties to the conflict have a duty -- to facilitate humanitarian access to populations in desperate need ... Right now, today," he said.
Preventing food supplies from getting to those in need by planting land mines, erecting barbed wire barriers, or other means was an "intentional tactic of 'surrender or starve'" that was in direct violation of the law of war, Kerry said.
Kerry urged the parties to work toward measurable progress on agreeing a ceasefire, increasing humanitarian assistance and developing a political transition plan as outlined in a Security Council resolution approved last month.
He said reaching a negotiated political settlement in Syrian would also undercut support for Islamic State militants across the region.