WASHINGTON -- The conflict between Sudan's military and the paramilitary Rapid Support Forces is "likely to be protracted" because both sides believe they can prevail militarily and have few incentives to negotiate, the top U.S. intelligence official said on Thursday.

Director of National Intelligence Avril Haines presented the bleak U.S. intelligence assessment of the fighting that erupted on April 15 in testimony before the Senate Armed Services Committee.

The assessment cast a shadow over international efforts to persuade the foes to end the violence, which has killed hundreds, prompted some 100,000 people to flee to neighboring countries and raised the specter of a worsening humanitarian crisis. Read full story

"The fighting in Sudan between the Sudanese armed forces and the Rapid Support Forces is we assess likely to be protracted as both sides believe they can win militarily and have few incentives to come to the negotiating table," Haines said.

The foes, she continued, both are seeking "external sources of support," which if forthcoming, "is likely to intensify the conflict and create a greater potential for spillover challenges in the region."

The ongoing violence, Haines warned, is worsening "already dire humanitarian conditions" and forced aid organizations to curtail operations amid growing fears of "massive refugee flows."

(Reporting by Jonathan Landay and Idrees Ali. Editing by Alistair Bell)