US gives ${esc.dollar}17 million more to Horn of Africa famine

* More than 12 million affected by drought in East Africa

* Investing in long-term food security essential -Clinton (Adds quotes, background)

WASHINGTON, Aug 11 (Reuters) - The United States will give an additional ${esc.dollar}17 million in aid for fighting famine in the Horn of Africa, including ${esc.dollar}12 million to help Somalis, U.S. Secretary of State Hillary Clinton said on Thursday.

Clinton said in a speech the new money -- which comes on top of ${esc.dollar}105 million in U.S. assistance announced on Monday -- would bring total U.S. humanitarian aid to the drought-hit region to more than ${esc.dollar}580 million this year.

With more than 12 million people affected by the worst drought in decades in Ethiopia, Kenya, Djibouti and Somalia, Clinton called on governments and donors to end the cycle of drought and famine across region by investing in agriculture.

She said the famine was the "most severe humanitarian emergency in the world today and the worst that East Africa has seen in several decades."

"And while we hurry to deliver life-saving assistance, we must also maintain our focus on the future by continuing to invest in long-term food security in countries that are susceptible to drought and food shortages," she told the International Food Policy research Institute.

About 3.6 million people in Somalia are at risk of starvation. The worst hit areas are controlled by al Shabaab militants, who have prevented aid from getting to people.

The rebels, who have waged a four-year insurgency against Somalia's Western-backed government, withdrew from Mogadishu at the weekend, opening the way for life-saving food aid to get to an estimated 100,000 who have fled to the capital in search of food and medicine.

The United States has relaxed anti-terrorism rules that threatened aid agencies working in areas controlled by al Shabaab, which is on the official U.S. list of foreign terrorist organizations.

Under the new guidelines, agencies will not be penalized if their activities "accidentally benefit" al Shabaab, which has allowed more aid to get into the hardest hit central and southern areas.

The new funding announced by Clinton brings to ${esc.dollar}92 million the amount of humanitarian aid being provided to Somalis by the United States.

Strengthening food security systems is key to avoiding hunger crises, Clinton said.

"Though food shortages are triggered by drought, they are not caused by drought, but rather by weak or non-existent agriculture systems that fail to produce enough food or market opportunities in good times and break down completely in bad times," Clinton said. (Reporting by Lesley Wroughton and Arshad Mohammed; editing by Mohammad Zargham)