Today's halting of aid convoys comes after hopes for peace were again dashed
Fighting has resumed in Syria after the week-long ceasefire brokered by the US and Russia came to an end yesterday.
The deal was designed to allow aid to reach civilians, but an attack on a convoy carrying humanitarian supplies after the ceasefire ended has sparked outrage.
The strike on 18 trucks killed 20 people, prompting the UN to suspend all aid convoys in the country.
However, there were difficulties and tension throughout the brief pause in the fighting.
The ceasefire begins but few, if any, on the ground believe it will hold.
Should it be deemed a success, the US and Russia say they will launch an unprecedented joint military operation against Islamic State and Jabhat Fateh al Sham jihadists.
Officials say the United Nations failed to deliver aid to Syrian civilians during the first day of the ceasefire because of security concerns.
UN Syria envoy Staffan de Mistura tells reporters in Geneva he has "no information about any UN trucks moving" and demands "assurances that the drivers and the convoy will be untouched".
UN Secretary General Ban Ki-moon urges Russia and the US to push all warring sides in Syria to allow safe passage for aid.
Lorries with a month's food supply for 40,000 people are stuck at the Turkish border, 48 hours into the ceasefire.
Russia accuses the US of covering up opposition violations in Syria as the now three-day-old deal comes under increasing strain.
The Russian defence ministry says Syrian regime forces have pulled back from the Castello road, a key access route into Aleppo, but that opposition groups have not followed suit.
The accusation comes as the first UN aid convoy bound for eastern Aleppo remains stuck due to the absence of permits from Damascus.
The UN envoy says the Syrian government has not provided the facilitation letters agreed as part of the ceasefire. As a result, 40 trucks of humanitarian supplies are stuck at the Turkish border.
The White House says it is deeply concerned that the Syrian government continues to block the flow of humanitarian help, despite a dip in the fighting.
The US-led coalition airstrikes - involving the British military - mistakenly kill 60 Syrian regime soldiers at Deir al Zor airport, while targeting IS positions.
The UN Security Council meets after Russia demands an emergency session to discuss the incident and accuses the US of deliberately jeopardising the ceasefire.
US ambassador to the UN Samantha Power hits back at Russia, accusing it of "cheap point scoring and grandstanding".
The US accuses the Syrian government and its ally, Russia, of carrying out airstrikes on rebel-controlled neighbourhoods and blocking aid from getting to besieged areas.
The Syrian military declare the ceasefire over and Syrian or Russian aircraft strike an aid convoy near Aleppo, reportedly killing 12 people.
It happens as world leaders gather at the UN in New York for their annual meeting, with the violence in Syria and the global refugee crisis top of the agenda.
The UK-based Syrian Observatory for Human Rights says later there were 35 strikes in and around Aleppo after the ceasefire ended.