At least 10 people were killed on Sunday when barrel bombs were dropped by regime forces on an opposition-held town in Daraa.
A fragile ceasefire between Bashar al Assad's regime and Syrian opposition forces that was brokered by the US and Russia last week has ended, with no word of a renewed truce on Monday.
From the outset, the week-long truce was marred by violations. Regime helicopters dropped four barrel bombs on an opposition-held town of Dael in the southern province of Daraa killing 10 people, including a child, the UK-based Syrian Observatory for Human Rights (SOHR) reported.
Airstrikes were also reported in Aleppo, Syria's largest city and former commercial hub. There was no confirmation as to whether or not the Syrian regime or its allied Russian airforce, both of which have oversight of Syrian airspace, were responsible.
The incidents came just a day after US-led coalition forces killed dozens of regime fighters south of Deir al Zor after mistaking them for DAESH terrorists, triggering criticism from Moscow.
Russia has backed the Assad regime since the war in Syria began in 2011, while the US has long called on Assad to step down.
The superpowers have been targeting DAESH with parallel military campaigns in Syria, forcing the terrorist group to retreat from swathes of land it took control of across the country in 2013 and 2014.
But the Syrian war has placed Washington and Moscow at loggerheads, with Russia seeking to prop up the regime while US-led coalition airstrikes on DAESH aim to pave the way for US-backed groups to take control.
Ceasefire ‘failed and ended'
A number of violations on both sides have threatened the ceasefire. Zakaria Malahifji, head of the political office of the Aleppo-based opposition group Fastaqim, told Reuters he believed the truce had "practically failed and has ended."
Malahifji also expressed doubt that UN aid trucks stuck on the Turkish border would reach besieged areas of eastern Aleppo. "There is no hope. It has been a number of days of procrastination. Every day there is a pretext. There is no hope of aid being delivered currently," he said.
Up to 300,000 people in the opposition-held parts of Aleppo are running low on vital supplies due to siege by the regime, which is yet to give permission to the 20-vehicle convoy waiting in the Turkish city of Gaziantep permission to cross into Syria.
"I am pained and disappointed that a United Nations convoy has yet to cross into Syria from Turkey, and safely reach eastern Aleppo," the UN Under Secretary General for Humanitarian Affairs Stephen O'Brien said in a statement.
Both sides have laid the blame on each other for ceasefire violations. On Sunday, Russian Defence Ministry spokesman Major-General Igor Konashenkov in an emailed statement accused "terrorists and the opposition" of using the ceasefire to "boost their forces and prepare for renewed hostilities".
Russia has also called for an emergency UN Security Council meeting after claiming over 60 regime fighters were killed by the US-led airstrikes on Saturday.
In turn, US Secretary of State John Kerry called on Russia to "stop the grandstanding, stop the showboating and get the humanitarian assistance going."
"Russia's client, Russia's supported friend, is the single biggest blockade to the ability to move forward here," Kerry told CNN in reference to the regime's failure to grant access to the UN aid convoy.