LONDON -- With more than 30 marathons this weekend and big events on the horizon, officials around the world are looking at security efforts in the wake of the fatal bomb blasts that shook Boston's race.
Britain was making last-minute efforts to tighten measures for former Prime Minister Margaret Thatcher's funeral on Wednesday at St. Paul's Cathedral, which is to be attended by hundreds of diplomats and dignitaries, including Queen Elizabeth II.
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Police with bomb-sniffing dogs were seen Tuesday afternoon around such landmarks as Big Ben, the Houses of Parliament and Trafalgar Square ahead of the Thatcher funeral, but officials said the searches were routine and unrelated to the Boston attacks.
Near the Pentagon's subway station in Washington, D.C., meanwhile, two military personnel toting guns and a security official in a bulletproof vest were spotted by one of the station's entrances.
Bomb-sniffing dogs and security officers were also deployed Tuesday to Chicago's Union Station.
Amtrak spokesman Marc Magliari said security had been beefed up at all its railway stations.
"No matter how many days, months or years pass without a major terrorist attack, it only takes one such attack to bring us back to the cruel reality," Interpol chief Ron Noble told The Associated Press early Tuesday, saying police around the globe would be on high alert.
Although security has been increased at some U.S. and European landmarks, overall terror threat levels have remained unchanged -- in contrast to other recent bombings and thwarted attacks in which terror threat levels were raised and travel warnings put in place.
Such warnings have been issued in the past when threats are considered imminent and with potential international links.
Threat levels also remained unchanged at U.S. defense installations at home and abroad, according to a Pentagon spokesman who requested anonymity because he was not authorized to speak to the press about security.
"The (Boston) attacks mean that we will be assessing our security protocols," said a British security official who spoke on condition of anonymity because he is not authorized to be publicly named. "There is some initial information coming out ... but it is too early to draw any conclusions. There doesn't appear at this point, however, to be a wider threat."
Security would be particularly tight for the big events in Britain, which has been at the heart of several terror attacks in the past decade, including suicide bombings in 2005 that killed 52 people. Several international terror plots have also been traced back to suspects in Britain.
Workers are inspecting some of the country's 4.3 million CCTV cameras in high-traffic areas around London to ensure views are unobstructed and equipment is functioning. Workers in an underground bunker monitor the footage around the clock.
Boosting security may also include adding manpower, increasing air visibility and securing public transport routes. Police and counterterrorism officials are also aggressively monitoring potential suspects.
More than 37,000 runners will be at Sunday's London Marathon, which will be attended by Prince Harry. Other marathons are also being held across the world this weekend in countries across Europe, in Japan, South Africa and around the United States.
London Marathon officials said the race would go on as planned but security was being evaluated. In Serbia, officials said they would raise their guard for the race.
"We will do our best so that this year the security level is even higher," said Dejan Nikolic, the organizer of Sunday's Belgrade Marathon.
Police in Linz, Austria's third largest city, said security was being tightened for the city's marathon Sunday, with police closely checking key points along the race, particularly the finish-line area.
Police Col. Heinz Felbermayr told reporters that his units are "totally prepared" for any eventuality, adding that while the Boston bombings should not be downplayed in relation to Linz `'they also should not be overly dramatized."
But organizers of the Hamburg Marathon said they did not plan any changes to their security measures for this Sunday's race. Hamburg police said they already have tight security for the marathon with 400 officers on hand.
Madrid authorities said Tuesday they will be meeting next week to decide if extra security measures are needed for the April 28 marathon.
Russian officials gave mixed signals Tuesday over whether they needed to increase security at key sporting events like the World Athletics Championship and the 2014 Winter Olympics.
The track and field championship, which takes place in Moscow on Aug. 10-18, is seen as a dress rehearsal for the Olympic Games in the Black Sea resort of Sochi.
One top sports official said security was being beefed up but others said Russia's take on Olympic security was already very robust.
Officials will speak with the organizers of the Boston Marathon to find out what more security precautions are needed, Mikhail Butov, secretary general of the Russian Athletics Federation, said Tuesday, adding that "when it's clear what actually happened (in Boston), we will draw our own conclusions."
Federation President Valentin Balakhnichev told the Interfax news agency that the Boston bombings on Monday revealed "problems" in ensuring security at outdoors events and expressed concern that it may inspire "other organizers of terrorist attacks."
Police and security services in Moscow are gearing up for "all possible emergencies" even though the athletics championships will be held in a confined space indoors at the Luzhniki Stadium.
Rio Olympic organizers said security would be "a top priority" as the city prepares for the 2016 Games.
The French Interior Ministry ordered local authorities across France to reinforce security measures already in place since the January intervention in the African nation of Mali began.
In New York, authorities deployed so-called critical response teams -- highly visible patrol units that move in packs with lights and sirens, -- along with more than 1,000 counterterrorism officers. Highly trafficked areas like the Empire State Building, Rockefeller Center, St. Patrick's Cathedral, the United Nations and the World Trade Center site were being especially monitored.
In Washington, Secretary of Homeland Security Janet Napolitano urged the American public "to be vigilant and to listen to directions from state and local officials."
At the White House, the Secret Service expanded its security perimeter after the attacks, shutting down Pennsylvania Avenue and cordoning off the area with yellow police tape. Several Secret Service patrol cars blocked off entry points, although the White House was not on lockdown and tourists and other onlookers were still allowed in the park across the street.
Security was also tightened at sports venues across the U.S., though most events were held as planned.
The exceptions were in Boston itself, where Monday night's NHL game between the Bruins and Ottawa Senators was postponed and Tuesday's NBA game between the Celtics and Indiana Pacers was canceled.
Officials announced plans for security reviews of upcoming marathons and road races in cities large and small.
Race officials for the Illinois Marathon in Champaign and Urbana, Illinois, said they were already fielding calls from worried runners and their families and planned to meet Wednesday to discuss more security measures such as bomb-sniffing dogs.