Sounding the alarm on behalf of more than 20 million people in South Sudan, Somalia, Yemen, and north-east Nigeria facing devastating levels of food insecurity, UN Secretary-General Antonio Guterres joined other top United Nations officials today calling for "strong and urgent" action from the international community to help the already-fragile countries avert catastrophe.

"Famine is already a reality in parts of South Sudan. Unless we act now, it is only a matter of time until it affects other areas and other countries. We are already facing a tragedy; we must avoid it becoming a catastrophe," said the Secretary-General, stressing: "This is preventable if the international community takes decisive action."

Briefing the press at UN Headquarters in New York alongside the UN Emergency Relief Coordinator, Stephen O'Brien, the UN Development Programme (UNDP) Administrator, Helen Clark, and by video conference, the Executive Director of the World Food Programme (WFP), Ertharin Cousin, Guterres said the UN needs at least US$4.4 billion by the end of March to avert a catastrophe.

"Despite some generous pledges, just US$90 million has actually been received so far – around two cents for every dollar needed. We are at the beginning of the year, but these numbers are very worrying," he said: "The lives of millions of people depend on our collective ability to act. In our world of plenty, there is no excuse for inaction or indifference."

In South Sudan, the United Nations and its humanitarian partners aim to assist 5.8 million people this year; in Somalia, 5.5 million people and in Yemen 8.3 million. In north-east Nigeria, humanitarians are reaching more than two million people with food assistance.

These four crises are very different, but are all preventable. "They all stem from conflict, which we must do much more to prevent and resolve," he said, urging all members of the international community to step up and do whatever is in their power, whether that is mobilising support, exerting political pressure on parties to conflict, or funding humanitarian operations.

"Saving lives is the first priority, but we are also looking to build longer-term resilience to shocks," Guterres said, noting that UNDP Administrator and the Emergency Relief Coordinator will set up a steering committee to link the UN Development Group and the Inter-Agency Standing Committee for humanitarian assistance to ensure a coordinated long-term approach.