Rebel fighters sit in a vehicle on the road between Misrata and Sirte, Moammar Gadhafi's hometown, on Tuesday. Tripoli, Libya (CNN) -- Tripoli's 2 million residents faced increasingly dire shortages of food and water Tuesday as rebels estimated the number of people killed during the past six months to be at least 50,000. "I cannot overstate the urgency of this moment," U.N. Secretary-General Ban Ki-moon said. "Time is of the essence." Ban said his goal was to get U.N. personnel on the ground "as quickly as possible." Sixty percent of Tripoli was without water or sanitation, Ban said. The European...