Yemen humanitarian situation likely to worsen with Saleh death: Jim Mattis

He said it could either push the conflict towards U.N. peace negotiations or make it an "even more vicious war."

"(But)one thing I think I can say with a lot of concern and probably likelihood is that the situation for the innocent people there, the humanitarian side, is most likely to (get) worse in the short term," Mattis said. He did not explain his reasoning.