The crisis in Sudan has "all the makings of a tragedy of global relevance", the UN's humanitarian relief boss said after visiting the country.
Martin Griffiths said attempts to broker a ceasefire in Sudan had stumbled over the "existential fact that those at war are keen to keep going".
Mr Griffiths said he has asked the warring parties for assurances that aid workers can travel in Sudan and that humanitarian planes will not be shot down.
"It's not as if we're asking for the moon," he said after visiting Port Sudan.
The UN has warned of a humanitarian disaster as fighting between Sudan's regular army and a paramilitary force continues. Many countries have evacuated their citizens from the country.
Mr Griffiths said he wanted to meet the warring generals "in the next day or so" to arrange for humanitarian aid.
Asked on BBC Radio 4's Today programme whether the two camps saw it as a "fight to the finish", he said: "We all worry about that."
The "tales of traumatic atrocity" that people have seen in Khartoum and Darfur "are pretty unparalleled ... that’s appalling, that will lead to a generational problem of reconciliation", he said.
"The second, I think, really deeply concerning aspect is the speed with which it’s going viral. The way in which all these efforts to get national or local or temporary ceasefires have all stumbled, presumably over the rigid existential fact that those at war are keen to keep going.
"It’s got all the makings of a tragedy of global relevance and global significance and that’s why this is an opportunity for the international community to show that we care about Africa."
