The Rio Olympic Games will take place from August 5-21 (AFP Photo/Yasuyoshi Chiba)

Rio de Janeiro (AFP) - Crime-plagued, cash-strapped Rio de Janeiro struck an optimistic note Tuesday with 30 days to go before becoming South America's first city to stage the Olympic Games.

Stadiums are all ready -- barring finishing touches -- and within weeks, Brazil expects to greet at least 500,000 tourists for the August 5-21 Games.

Brazil's Olympic committee boss Carlos Nuzman celebrated the milestone in an epic seven-year effort to transform Rio from a beautiful but crumbling city to a glittering stage for the world's most-watched event.

"We are sure that this will be an unbelievable party and everyone will love it," Nuzman told a press conference alongside Mayor Eduardo Paes. "Rio has seen the greatest transformation of a city."

Some 10,000 athletes will compete over 19 days in Rio, ranging from familiar sports icons such as sprinter Usain Bolt and swimmer Michael Phelps to the stars of Olympic newbie sport rugby sevens and golf, which returns after more than a century's absence.

But despite growing excitement in the sporting world and visible progress at Olympic sites in Rio, a mounting series of problems are overshadowing the Games.

- Troops on streets -

Terrorism is a serious concern given the Islamic State group's growing geographical reach, with mass attacks and suicide bombings claimed by or blamed on the group in Baghdad, Istanbul, Bangladesh and Florida in the past month alone.

The authorities will deploy 85,000 police backed by army soldiers, the first units of which deployed in camouflage uniforms Tuesday on Rio's streets. That's twice as many security personnel as used in the 2012 London Olympics.

Brazil's distance from jihadist hot spots, coupled with the country's absence from wars, is seen as a major plus. "All the international security agencies consider that we are not likely to have a terrorist act," Justice Minister Alexandre de Moraes said Tuesday.

However, Rio faces its own serious violent crime that has embarrassed Olympic organizers trying to change the city's image.

New government statistics released Tuesday showed a dip in murders, which have been on the rise all year, totaling 2,083 in the first five months across Rio state.

But street muggings have exploded this year, with 9,968 cases in May, up almost a third on May last year -- the equivalent of 14 robberies an hour.

Police -- heavily criticized by human rights groups over their brutal tactics in slums known as favelas -- are themselves coming under deadly fire. More than 50 Rio state police have been killed this year.

Deepening the sense of crisis, Rio state, which is near bankruptcy amid Brazil's crippling recession, has for months been unable to pay full salaries to police and other emergency services workers, teachers and pensioners.

On Monday, police officers greeted travelers in Rio international airport's arrival hall with a banner reading "Welcome to Hell" and warning that security cannot be guaranteed in the city.

A 2.9 billion reais ($883 million) emergency bailout from the federal center is due to be distributed this week, easing tensions.

- PR battle -

As the torrent of bad publicity grows, Rio's mayor and Olympic organizers have fought back.

Paes said Tuesday that improvements to Rio are on par with those credited with bringing huge urban renewal to Barcelona in 1992. "The Rio 2016 Games can also transform the city," he said.

And Nuzman said the fact that Rio was succeeding in such hard circumstances showed the Olympics are not just for developed countries. "I'm a firm defender of organizing the Olympics on all continents, the poorest and the richest," he said.

Despite the decision of several athletes, notably high profile golfers, to pull out of the Olympics because of fear over the mosquito-transmitted Zika virus, the authorities insist there are no serious health risks.

Zika can trigger birth defects in babies born to infected mothers, but in most cases causes little beyond flu-like symptoms -- and August is a month with few mosquitoes.

On the security issue, although Paes acknowledges problems, he blames the state government, not the city.

"This is the most serious issue in Rio and the state is doing a terrible, horrible job," he told CNN.