LONDON -- From London to Sochi to Rio de Janeiro, the deadly bomb attacks on the Boston Marathon raised new concerns Tuesday over safety at major sports events around the world, including the Olympics and World Cup.
The twin bombings near the marathon finish line that killed three people and injured more than 170 people brought into sharp focus the security challenges facing next year's Winter Olympics in Sochi, Russia, the 2014 World Cup in Brazil and the 2016 Summer Games in Rio.
"We are very, very concerned," senior IOC member Gerhard Heiberg of Norway told The Associated Press. "Security is priority No. 1, no question about it."
More immediate is the security planning for this weekend's London Marathon, which attracts more than 30,000 runners and half a million spectators. Organizers said they were reviewing security for Sunday's race -- one of the world's six major marathons -- but the event will go ahead as scheduled in a display of unity with Boston.
"The best way for us to react is to push ahead with the marathon on Sunday, to get people on the streets and to celebrate it as we always do in London," British Sports Minister Hugh Robertson said. "We are absolutely confident here that we can keep the event safe and secure. ... The best way to show solidarity with Boston is to continue and send a very clear message to those responsible."
The London Marathon, which takes in some of the city's most recognizable landmarks, draws many of the world's top marathoners as well as tens of thousands of amateur and "fun" runners who raise money for charity. Prince Harry, patron of the marathon's charitable trust, is scheduled to attend Sunday's race and make the presentations to the winners.
"When you have an event of any nature -- a marathon, parade -- it's only as safe as the city itself," race chief executive Nick Bitel said. "If it's not held in a stadium, you can't do a lockdown like you may do in a building."
Also taking place Sunday is the Bahrain Grand Prix, a Formula One race that faces its own security issues after a series of explosions, including a gas cylinder blast that set a car ablaze in the Gulf nation's financial district.
A Human Rights Watch report alleged that Bahrain authorities rounded up activists living around the track in a bid to "silence" dissent ahead of the race. Protesters, carrying portraits of people killed in the nation's nearly three-year uprising, are calling for a boycott of the race.
Security for the Olympics, meanwhile, has been paramount ever since the attacks by Palestinian gunmen that killed 11 Israeli athletes and coaches at the 1972 Munich Games.
The focus now falls on Sochi, a Black Sea resort that will host Russia's first Winter Olympics next February. Security was already a concern because of Sochi's proximity to an Islamic insurgency that spread across southern Russia after separatist wars in Chechnya.
"Naturally, we're beefing up security measures," Russian Sports Minister Vitaly Mutko said in remarks carried by the R-Sport news agency.
IOC vice-president Thomas Bach, who was on his way to Sochi on Tuesday for an international journalists' conference, said the attacks in Boston reinforced the IOC's policy that safety is paramount for any Olympics.
"I'm sure that this malicious attack will lead the public authorities to have another look at all security measures," Bach told the AP by telephone. "While it is too early to draw any final conclusions, we have full confidence in the Russian authorities. They have already analyzed the overall situation and I'm sure they will take this event into account and take the necessary measures."
Heiberg, who organized the 1994 Winter Games in Lillehammer, Norway, and now chairs the IOC's marketing commission, said security concerns had been heightened since the Sept. 11, 2011, terror attacks in the United States. Since then, Olympics have passed off peacefully in Salt Lake City, Athens, Turin, Beijing, Vancouver and London.
"So far we have been lucky in the Olympics but what happened in Boston reminds us that we cannot take it easy, we have to continue and we have to plan for not only the possible but also the impossible," Heiberg said. "We are taking it extremely seriously in Sochi, working very hard with the Russian authorities."
The Russian Interior Ministry said Tuesday it has fully deployed the police force that will be in place during the Sochi Olympics and has conducted regular checks of all venues to make sure they are protected.
Alexander Konovalov, head of the Institute of Strategic Assessment and Analysis, an independent think-tank, said international terror groups could be encouraged by the carnage in Boston to plot against the Sochi Olympics.
"The terrorists' strategy is to create a sense of panic and leave an impression that they can strike any target, no matter how tightly it's protected," Konovalov said. "The Olympics would make a highly desirable goal for terrorists, offering the maximum publicity."
Russia is also hosting one of the biggest international sports events of 2013 -- the world track and field championships in Moscow on Aug. 10-18.
"Our security measures are tough as they are," said Mikhail Butov, secretary general of the Russian Athletics Federation. "But when it's clear what actually happened (in Boston), we will draw our conclusions."
Guarding the Olympics is a massive operation covering 17 days of competition in numerous outdoor and indoor venues. Not only are sports facilities at risk, but so are the public areas where fans and spectators congregate. At the 1996 Summer Games in Atlanta, a backpack bomb exploded at Centennial Olympic Park, killing one person and injuring more than 100.
"The balance is not easy," Heiberg said. "Of course, you can provide security but we don't want to show the world pictures of soldiers and police with guns and so on. It's the same for Rio and all the others to come."
Rio organizers, who will be hosting the first Olympics in South America, said they are working with the government to "deliver safe games in 2016."
The city has won kudos for its crackdown on once-endemic drug violence in preparation for hosting the World Cup and Olympics. But safety has been a big topic in Rio recently after an American woman was gang raped and beaten aboard a public transit van while her handcuffed French boyfriend looked on helplessly.
Ahead of next year's World Cup, Brazil is hosting the Confederations Cup in June. The warm-up tournament featuring eight teams will be played in six cities across the country and is seen as a big test for organizers in all areas.
On Sunday, two fans were shot to death on their way to a match meant to test the facilities at a World Cup stadium in northeastern Brazil. Rival supporters were suspected in the killings.
The terror threat was considered high for last year's London Olympics, where overall security costs rose above 1 billion pounds ($1.6 billion). London was hit by terrorism in 2005, when 52 people were killed in attacks by suicide bombers on the city's transportation network.
London's huge security operation included thousands of police and military troops and deployment of warships, surveillance aircraft, sniper-carrying helicopters, fighter jets and missile batteries on rooftops.
Denis Oswald, who headed the IOC co-ordination commissions for the Athens and London Olympics, said the games remain a potential target wherever they are held and the Boston attacks do not radically change the security planning for Sochi or Rio.
"Each case has to be studied," Oswald said. "It could be new ways or new systems put in place. We just have to make sure these types of cases are covered by the security system. We have to be 100 per cent vigilant and never neglect any possibility."
Associated Press writers Natiliya Vasilyeva, Vladimir Isachenkov and Yelena Yegorova in Moscow, and AP Sports Writer Tales Azzoni in Sao Paulo, Brazil, contributed to this report.