LONDON // With more than 30 marathons being held this weekend and big events on the horizon, officials around the world are boosting their security measures.
Britain was tightening security for former prime minister Margaret Thatcher's funeral today at St Paul's Cathedral.
Russian sports officials said yesterday they would increase measures for the Winter Olympics and other events.
And police in some major US cities were monitoring landmarks, government buildings, transit centres and sporting events. The public has been urged to report any suspicious activity.
"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," said the Interpol chief, Ron Noble.
Although security has been increased at some US and European landmarks, overall terror threat levels have remained unchanged, in contrast to other recent bombings and thwarted attacks.
"The [Boston] attacks mean that we will be assessing our security protocols," said a British security official.
"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 was particularly tight for the big events in Britain, which has been the target 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 closed-circuit TV cameras in high-traffic areas around London to ensure they are working and views are unobstructed. Staff in an underground bunker monitor the footage around the clock.
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Boosting security may also include adding manpower, increasing air visibility and securing public transport routes.
Police and counter-terrorism officials are also intensely monitoring possible suspects.
More than 37,000 runners will be at Sunday's London Marathon. Other endurance races are being held this weekend in countries across Europe, in Japan, South Africa and around the US.
London Marathon officials said the race would go on as planned but security was being evaluated.
In Serbia, officials said they would also raise their guard for the Belgrade Marathon on Sunday.
Organisers of Japan's Nagano Marathon said they would go ahead with the race as planned this weekend.
"We will have closer communications with police and security officers to make sure the race takes place without any problems," said Makoto Yajima, a spokesman for the organisers.
More than 650 police and security officers will be involved, Mr Yajima said, adding that this number had been unchanged by the tragic events in Boston.
Tourists aboard the Eurostar train that crosses the English Channel to London said they still planned to watch the London Marathon on Sunday.
"All said and done, I'll still keep an eye out," said Jim Gullack, 52, of Dallas.
Russian sports officials said they would beef up security at sports events and the 2014 Winter Games.
The World Athletics Championship takes place in Moscow on August 10 to 18, and the event is seen as a dress rehearsal for the Winter Olympics that will be held in the Black Sea resort of Sochi.
Vitaly Mutko, the Russian sports minister, described the attack in Boston as "a grave signal".
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.
Since then, armed soldiers have patrolled subway stations, monuments and city streets.