ADDIS ABABA, Ethiopia -- The U.S. has boosted its emergency food aid to Ethiopia by nearly $100 million to combat one of the worst droughts in decades, the U.S. Agency for International Development announced Sunday.

The aid is urgently needed to head off a humanitarian disaster brought on by the El Nino climate phenomenon that has affected seasonal rains, USAID administrator Gayle Smith said.

"The funding for this is not where it needs to be and we are up against very tight timelines," she said at a briefing during the annual African Union summit, which ended Sunday. "This is the worst El Nino in history and it has affected the African continent in particular, most dramatically in Ethiopia where 11 million people have been affected."

On Sunday, U.N. Secretary-General Ban Ki-moon visited Ethiopia's Ziway-Dugda region, one of the areas hit by drought, where he was welcomed by thousands of residents in the streets of Ogolcho, the biggest town there. Ban visited a food distribution centre, and met with farmers and relief workers.

"This challenge may last some time. With the continued and concerted effort, I think we can overcome. And I (am) very much moved to have seen how hard the people are working," Ban said.

The El Nino warming over the Pacific Ocean has been particularly severe this year with spring and summer rains failing in Ethiopia and causing crops to fail and killing livestock.

The $97 million from USAID will include about 176,000 metric tons of food to be distributed to 4 million people. Since October 2014, the U.S. has given $532 million in humanitarian aid to Ethiopia.

The U.N. has issued an international appeal for $1.4 billion in emergency funding for Ethiopia, of which less than half has been met by donors.

Smith said the U.S. will urge other international donors to step in and support Ethiopia's efforts to deliver food aid and preserve the development gains of the last two decades. Donors have been distracted by crises in Syria, South Sudan, Yemen and the European migration issue, she said.

Ethiopia was famously devastated by a drought in the 1980s exacerbated by a civil war that killed hundreds of thousands. Despite the severity of the current drought, the existing government safety net is expected to prevent another famine, according to aid officials.