The United Nations has appealed for a further $1.4 billion to provide humanitarian aid to more than 12 million people in drought-stricken countries in the Horn of Africa.

The U.N. humanitarian aid agency said Friday that if aid response does not increase along with the region's rising needs, famine in two regions of Somalia could spread throughout the rest of southern Somalia within one to two months.

In a statement, the U.N. said thousands of Somalis every day seek refuge in Ethiopia and Kenya to flee violence and soaring food prices — the result of the worst drought in 60 years.

Clashes have broken out between al-Shabab militants and government and African Union troops, as the militants try to block the aid from being dispersed.

The U.N. says the crisis is expected to peak in August and September, and the number of people needing aid could increase by as much as 25 percent.

Earlier Friday, the U.N. children's agency said 1.25 million children are among the 3.7 million Somalis in urgent need.

Also Friday, a second plane from the U.N.'s World Food Program landed in the Somali capital, Mogadishu, with a load of nutritional supplements.

The al-Qaida-linked group al-Shabab has banned U.N. aid. The militants are trying to turn Somalia into a staunchly Islamic state and already control much of the country.

The U.N. has declared a famine in two sections of southern Somalia, both of which are al-Shabab strongholds. The U.N. is expected to airlift more aid this week to eastern Ethiopia and northern Kenya, near the Somali border, where thousands of Somalis are filling overcrowded refugee camps.