The humanitarian aid flight crashed into a mountain early Tuesday at an elevation of about 10,000 feet during the region's rainy season, making efforts to reach the crash site difficult, a United Nations spokesman in New York said.

"However, given that aerial reconnaissance found that the plane suffered an extremely violent impact, the likelihood of survivors is low," U.N. spokeswoman Michele Montas said.

Several U.N. personnel were among the passengers.

The plane, which was en route from Kisangani to Bukavu, was operated by Air Serv, a U.S. carrier that provides air transport for the international humanitarian community. It was beginning its landing approach when it crashed several miles from Bukavu airport, the U.N. official said.

Montas said efforts to reach and work on the wreckage site could last several more days. She said two U.N. mission helicopters carrying 25 U.N. military and South African special rescue team members had left for the site.

Secretary-General Ban Ki-Moon, meanwhile, expressed his sorrow about the accident.