WASHINGTON (Reuters) – President Barack Obama Barack has chosen retired Air Force General Scott Gration as his special envoy to Sudan, a U.S. official said on Tuesday, in the midst of a worsening humanitarian crisis in its Darfur region.

Sudan expelled 13 aid groups after the International Criminal Court charged Sudanese President Omar Hassan al-Bashir with war crimes in Darfur, where 4.7 million people rely on foreign assistance for food, shelter and protection from fighting between rebels and government-backed forces.

“The president and secretary of state are on the verge of appointing Gration to the job,” an administration official said. The official, who spoke on condition of anonymity, said the formal announcement would likely come on Wednesday.

“He’s someone with deep experience in the region, who has personal and professional relationships with key leaders and most importantly has a close personal friendship with the president and has his ear,” the official said.

Gration, a decorated fighter pilot, was often seen with Obama on the presidential campaign trail last year. They got to know each other when Obama visited Africa in 2006 while still a senator. During that trip they visited Darfur refugees in Chad, which neighbors Sudan.

The son of missionary parents, Gration was raised in Africa and is fluent in Swahili.

Obama has pledged U.S. help in addressing the humanitarian crisis in Darfur, where U.N. officials say as many as 200,000 people have died since rebels rose up against the Khartoum government in 2003.

The United States increased pressure on Sudan on Tuesday to readmit expelled foreign aid groups. Secretary of State Hillary Clinton said Sudan’s President Bashir would be responsible for “every single death” caused by their expulsion.

“This is a horrendous situation that is going to cause untold misery and suffering for the people of Darfur, particularly those in the refugee camps,” Clinton said.