A top United Nations official has urged word leaders to reform the humanitarian aid system and uphold international humanitarian law ahead of a key summit.

Speaking on the eve of the first World Humanitarian Summit in Istanbul, Deputy Secretary-General Jan Eliasson said the gathering was a "wake-up call for action."

He said Sunday that "there is a huge need for us to show solidarity with those who are affected by natural disasters and man-made disasters."

Eliasson urged leaders to defend international humanitarian law which is being flouted in Afghanistan, Syria and Yemen.

The event is a bid to boost the response to what the United Nations calls the worst humanitarian crisis since World War II.

Sixty-five heads of state and government representatives from 180 countries are expected to attend.