Reports of an intense bombing campaign targeting several areas in the rebel-held part of Aleppo city signal an end to the fragile ceasefire between the Syrian government and rebel groups.
The war in Syria is five years old and shows little sign of abating. The ceasefire was a small step forward in a conflict which continues to escalate and draw in more actors.
Does the recent ceasefire provide hope of a resolution, even if it failed?
What conditions did the ceasefire include?
Russia and the US brokered the ceasefire, which began on September 12. It included rebel groups and government troops abiding by a cessation in the conflict.
The ceasefire did not include Islamic State (IS), otherwise known as Daesh. It was hoped that if the ceasefire was a success, the two sides could unite to fight them.
The two sides had said that if it held for seven days, it would be followed by the establishment of a Joint Implementation Centre for both countries to co-ordinate the targeting of IS and al Qaida-linked militants.
Why did it collapse?
As is often the case in a broken ceasefire, all parties are blaming each other.
On Monday, the opposition reported 254 violations by government forces and their allies since the truce started on September 12. Syrian state media said there were 32 violations by rebels on Sunday alone.
The Syrian government declared the ceasefire over on Monday, blaming the country's rebel groups for undermining the agreement.
The US accused Syrian president Bashar Assad's government, aided by Russian planes, of striking an aid convoy in Aleppo later that day which killed 20 people.
Assad has rejected US accusations that Syrian or Russian planes struck the aid convoy or that his troops were preventing food from entering the city's rebel-held eastern neighbourhoods, blaming the US for the collapse of the ceasefire.
In an interview with the Associated Press in Damascus, Assad also said deadly US air strikes on Syrian troops last week were intentional, dismissing American officials' statements that they were an accident.
Is there hope for a longer ceasefire?
US secretary of state John Kerry has proposed the grounding of aircraft to protect aid convoys, saying: "To restore credibility, we must immediately ground all aircraft flying in those key areas in order to de-escalate the situation and give a chance for humanitarian assistance to flow unimpeded."
Whether the Russian and Syrian side of the negotiating table will agree to this is unknown.
After days of increasing violence in Syria, Kerry and Russian foreign minister Sergey Lavrov were set to hold more talks on Friday in a bid to try to resuscitate the ceasefire.
But after three days of private and public diplomacy on the sidelines of the United Nations General Assembly, Kerry bluntly told reporters: "We can't go out to the world and say we have an agreement when we don't."
Some collapsed ceasefires increase hostility and some open the door for more efforts to end conflict; it is too early to tell what the outcome will be for Syria.