UN Secretary General Ban Ki-moon has urged Russia and the US to push all warring sides in Syria to allow safe passage for desperately needed aid.

Lorries with a month's food supply for 40,000 people are stuck at the Turkish border, 48 hours into a ceasefire.

Getting aid to civilians in besieged areas like the rebel-held eastern half of the city of Aleppo is a priority.

But disagreements between warring sides and concerns about safety are delaying emergency deliveries, the UN says.

Criticism has also been levelled at President Bashar al-Assad's government for trying to control aid flows.