Updated

Police backed by helicopters raided a notorious Rio shantytown and killed 19 suspected drug traffickers in pitched gunbattles.

Police recovered 13 bodies and six more were left, apparently by the drug gangs, inside a van parked outside a police station near the scene of Wednesday's fighting.

The assault led to the worst urban combat in a two-month siege of the Alemao shantytown, where fighting has killed at least 40 people and injured more than 80 since May.

Authorities sent 1,350 officers and elite federal police to the slum long ruled by gangs. They were met with grenades and fusillades from automatic weapons.

Eleven people were wounded, including innocent bystanders, gang members and one police officer.

But all those killed were suspected members of gangs that dominate the area's thriving street-corner drug trade, said Rio de Janeiro state security chief Jose Mariano Beltrame.

"No innocent people were killed," Beltrame told reporters, adding that the operation was a "bitter remedy" but would continue indefinitely.

Parents frantically tried to protect their children from the gunfire after classes were suspended. Gang members dumped oil on streets to try to prevent armored cars from entering and police had to use a backhoe to remove a truck blocking the entrance to the adjacent Grota shantytown, where some of the heaviest fighting took place.

Wednesday's daylong battle was the biggest police show of force since the killing of two officers on May 2 touched off repeated exchanges of gunfire. Police took over low-lying areas of the hilly Alemao area, then moved up several of the narrow alleys that line the hillside shantytowns.

Photographers captured images of slum dwellers leaning over the body of a man shot dead in the street, and of other men carrying a crying young woman with a gunshot wound to the leg.

"It's tough," said Luiz Claudio dos Santos, a community leader. "We have people shot here at the hospital from all over the Alemao complex."

Authorities said Wednesday's death toll could rise because police believe some bodies had not been recovered.

Police said they entered the slum to serve arrest warrants and seize drugs and arms, but did not disclose whether arrests were made.

Beltrame denied the operation was related to the upcoming Pan American Games, one of Latin America's most important sporting events. Security is a key concern for the July 13-29 games, when thousands of athletes and hundreds of thousands of spectators are expected in the city.

Officials said that 6,000 additional police will boost security for the games.