By MEGAN JANETSKY MEXICO CITY (AP) — U.S. Ambassador Ken Salazar rejected accusations by Mexico’s president that the U.S. was partly responsible for a surge in cartel warfare in northern Sinaloa over the weekend. Sinaloa has been eclipsed by violence as two warring factions of the Sinaloa cartel have clashed in the state capital of Culiacan in what appears to be a fight for power since two of its leaders were arrested in the U.S.