The Libyan war may be over, but rivalries rage on among some regional militias, leading to a mutual distrust that poses a challenge to the new leadership.Earlier this week, the rivalry was evident when dozens of fighters clashed at a Tripoli hospital in what residents said was the biggest armed confrontation in the capital in weeks.Clashes erupted at 2 a.m. Monday when a half dozen former rebels from Zintan city in the western mountains stormed the hospital, according to doctors.Some of the former rebels were drunk, and demanded staff hand over a wounded fighter shot earlier that day, according to the doctors, who spoke on condition of anonymity for safety reasons.The patient and the body of a dead fighter had been taken to the hospital earlier, the doctors said, and the former rebels wanted to kill the wounded man.Hospital staff declined to hand over the patient, who was undergoing surgery.Tripoli fighters in charge of hospital security forced them out , but not before the returning fighters shot rounds in the hospital.Both groups called for backup, which arrived as fighting raged around the hospital grounds until 5 a.m. Witnesses said both sides were using heavy machine guns and anti-aircraft guns.Walls near a hospital entrance were riddled with bullets holes, and nearby glass doors and windows were shattered. Across the street, bullets pierced through the walls of two buildings.There were no deaths from gunshots, but medical staff said three patients died of stress-related causes that they linked to the fighting.At least three of the Tripoli fighters were wounded in the clashes, according to Salem Abaza, who is in charge of hospital security. He described it as the most serious incident of infighting so far.Accounts differed over how the three-hour battle concluded, but at least three witnesses said it ended after calls from a local imam and senior commanders from both groups talked by phone with their men.Tripoli fighters said Tuesday they are concerned about the rising tensions among the various groups, which are increasingly divided along regional allegiances."We are concerned, as you can see, every day there is fighting between the rebels, this is something we don't want, we want a united Libya," said fighter Tammam Basheer.The scene on Tripoli's streets these days -- heavily armed men brandishing guns and racing across the city with no central command and little or no accountability -- has raised concerns among residents."There are no security forces, everyone is running their own group, their own brigade, and they all control Tripoli," said Tripoli militia member Taha, who did not provide a second name.Disarming tens of thousands of fighters who brought down ruler Moammar Gadhafi and bringing them under control is a top challenge for the fledgling interim government.Acting Prime Minister Abdurrahim El-Keib is expected to present his Cabinet within two weeks.Military officials downplayed the tensions among the various militias, and say their biggest challenge is rebuilding the military."We would like to reorganize our army again," said Col. Ahmed Bani, the National Transitional Council's military spokesman. "When we have a great and strong army, we are safe. We will save our dreams, we will save our democracy, our borders."At the Tripoli hospital, staff spoke of other recent incidents of intimidation by armed militiamen and called on authorities to provide protection and pull the weapons off the streets."We are really afraid, we do not want stethoscopes to be fighting guns," Dr. Ali Osman said.