RIO DE JANEIRO (Reuters) - Police in Rio de Janeiro gave drug traffickers holed up in a hillside slum an ultimatum on Saturday to turn themselves in and help put an end to a wave of urban violence that has killed at least 46 people. More than 1,000 police and army officers surrounded the shantytown as part of an unusually determined effort by security forces to take control of territory that has long been controlled by drug gangs. Authorities have cast the battle as part of a larger effort to pacify the city ahead of the Olympic Games in 2016. Drug gangs have fought back by setting fire to around 100 cars and buses and firing on police with automatic weapons. There is not the slightest chance traffickers can win in this war in Alemao, head of the military police Sergio Duarte told reporters, referring to the surrounded shantytown. We are in position to invade Alemao at any moment. Its better they give themselves in now and bring their weapons while theres still time, because when we invade, its going to be more difficult, he said. Duarte did not give a date or time for the offensive. The suspected traffickers fled to Alemao from the Vila Cruzeiro slum after police invaded it earlier this week and took control. Local media say officers have since found guns and grenades there and a machine to count bank notes from the traffickers lucrative illegal trade. Police are now searching vehicles and pedestrians entering Alemao. Gang members inside the slum have opened fire on the security forces to try to ward them off, injuring 10 people on Friday and Saturday, including a Reuters photographer. Two men were arrested after trying to flee Alemao on Saturday. Police said they were believed to be gang leaders involved in the shooting down of a police helicopter earlier this year. The latest wave of violence has cast some doubts over whether the city is safe enough to host the 2014 soccer World Cup and the 2016 Olympics, even though sports authorities have said they trust the governments security measures. The military police said an area had been designated within the slum, or favela as they are locally known, where the gang members could surrender with their arms placed on their head, and said it was their only option to avoid an offensive.