A ceasefire aimed at allowing civilians to leave the ruined city of Aleppo in Syria has collapsed.
Thousands of people are now trapped by heavy shelling and gunfire.
Pro-government forces and rebels are accusing each other of breaking the truce.
Martin Chulov from The Guardian Newspaper - explains the significance of Aleppo: "It’s central to who will win the war.
"Very near victory comes as elsewhere in the country and rebellions and interactions have been instantly quelled.
"But this is by far and away the biggest, if this fails as it almost most certainly will, than that only leaves idlib and rucca which is in ISIS control but idlib is the only other city in Syria which is outside the controlc of the regime."