A leading opposition figure declared Syria's ceasefire a "big lie" on Monday, since it has failed to deliver humanitarian aid to hundreds of thousands of desperate people in need.
Although the ceasefire, brokered by the US and Russia, did manage to significantly reduce violence in its first days since it went into effect last week, it now looks set to collapse.
On Sunday, there were reports of the first airstrikes on rebel-held eastern Aleppo city.
"This week of truce did not last and it failed to achieve its goal in sending humanitarian assistance," George Sabra, a senior member of the opposition High Negotiations Committee (HNC), told dpa. The truce effort has "lost credibility," he added.
The Syrian state-run news agency SANA reported that the ceasefire had lasted seven days, until midnight, "with the army reserving the right to respond decisively using all types of firepower to any breach by armed groups." It did not report on an extension of the truce.
The US-Russian agreement for a ceasefire in Syria stipulated that it was to last for seven days and if successful, the two countries would consider carrying out joint strikes against targets such as al-Qaeda-linked fighters.
Russia, a staunch backer of President Bashar al-Assad, has been demanding that the US separate moderate rebel forces from jihadist groups, something Washington has struggled with. Extremists are fighting alongside rebels against al-Assad, as the opposition relies on the strength of hardline groups.
The truce was also meant to help deliver needed aid to hundreds of thousands of people in hard to reach and besieged areas.
Some 40 trucks ready to transfer aid assistance to eastern Aleppo, where 300,000 people are living under siege, are still stuck at the Turkish border waiting for permission from the Syrian government.
Meanwhile, the Syrian Red Crescent has managed to bring in 12,000 food parcels to Moudamyat al Sham, a rebel-held area located at the outskirts of the capital Damascus, state-media reported. The rebel-held town of Talbiseh, north of Homs, also successfully received an aid delivery.
Turkey's President Recep Tayyip Erdogan, a key backer of the armed opposition in northern Syria, repeated his call for a no-fly zone in the north.
This call has already been rejected by policy makers in Washington as difficult to implement, especially since Russia began an air campaign last year.
Russia and the US are further at odds since Moscow reported an airstrike by the Washington-led coalition killing dozens of Syrian soldiers. The US says it is investigating, but if true, the strike was aimed at the Islamic State extremist group.