The African Union has postponed a conference to raise money for the millions affected by drought and famine in the Horn of Africa.

An AU statement Thursday said the conference in Ethiopia's capital has been moved from August 9 to August 25.

The statement did not give a reason for the delay. The Associated Press quotes a senior AU policy adviser as saying the later date would allow heads of state to attend.

The United Nations has appealed for $1.4 billion to help the drought victims.

On Wednesday, the U.N. said the drought has turned to famine in three more areas of southern Somalia. It said famine conditions will likely spread to more areas and and could last until December.

Somalia is at the center of the worst drought to hit in the Horn of Africa in 60 years. The United Nations says more than 12 million people in the region are in need of food aid.

At a hearing in Washington, U.S. officials and private experts accused militant group al-Shabab of preventing people from fleeing the famine-stricken areas.