LONDON — Rio de Janeiro has a tough battle ahead combatting security problems before the 2016 Olympics, the Brazilian city's mayor said Monday.

The challenges facing mayor Eduardo Paes since winning the Olympic vote earlier this month were underscored by a wave of violence over the weekend that left 14 people dead.

"We never hid our problems during the bid process — we always told people we had problems and we are facing the problems," Paes told the Global Sports Industry Summit in London. "We still have a lot to do, we have a long way to go and what happened this weekend showed that."

The firefight between rival gangs raged Saturday in a city slum about five miles southwest of one of the zones where the Olympics will be held in seven years.

During the gang battle, bullets hit a police helicopter hovering overhead and it crashed in a fireball onto a football field, killing two officers and injuring four more.

When Rio was chosen over Chicago, Madrid and Tokyo to host the Olympics in the Oct. 2 vote, its bid was the only one that pointed to security concerns.

"We are being tough with these problems," Paes said. "We are sure by 2016 we will deliver the games and hopefully in a way that the city will be more peaceful and secure for all our citizens.

"We worry about security for our citizens, for our everyday lives, for the visitors that come on a regular basis. That's our challenge and things are moving forward. ... The violence we face in Rio will be much, much better by 2016."

Craig Reedie, a member of the International Olympic Committee's executive board, said the significance of gang violence should not be overstated.

"Rio is a big city," Reedie told the conference. "I deeply regret what happened in Rio recently but I have to say that it pales into insignificance compared to what happened in London in 2005."

A day after London won the right to host the 2012 Olympics, four suicide bombers attacked the city's subway and bus network, killing 52 people.