The most impoverished nations that need the most help should be assisted by the United Nations and the International Monetary Fund. No one country should foot the bill to assist another from the clutches of poverty. Eliminating poverty is the bane of all humanity, not just one organization. If any single entity could eradicate poverty on this planet, the United Nations is it.
No, increasing aid from the UN to poor nations is not morally justified, because the aid is often abused. It is better if each individual nation gives aid to these countries, because the individual nations can offer better oversight than the United Nations can. It is always kind to help the poor, but without oversight, there is no guarantee that the aid is helping.