LONDON — From the World Trade Center and Times Square in New York to the White House and sports venues across the country, police patrolled in packs and deployed counterterrorism teams Monday as security was stepped up after explosions at the Boston Marathon.
Worries also reverberated across the Atlantic, where an already robust security operation was being beefed up for Wednesday’s ceremonial funeral for former Prime Minister Margaret Thatcher. The event at St. Paul’s Cathedral, to be attended by Queen Elizabeth II and other dignitaries, calls for a procession through the streets of London, with Thatcher’s flag-draped coffin carried on a horse-drawn carriage.
British police were also reviewing security plans for Sunday’s London Marathon — the next major international race — because of the bombs that were detonated at the Boston Marathon finish line Monday.
Last year, some 37,500 athletes competed in the London Marathon, with many more watching the event.
London long has been considered a top target for international terrorists, with the government saying the threat level is ‘‘substantial.’’ In 2005, a series of suicide attacks on the public transport system in the British capital killed 52 people.
The blasts in Boston sparked alarm bells in Britain, where a massive security operation was put in place last summer to protect the successful London Olympics.
Chief Superintendent Julia Pendry, police commander for the London race, said Monday that ‘‘a security plan is in place for the London Marathon. We will be reviewing security arrangements in partnership with the London Marathon.’’
Across the United States, security was tightened at landmarks, government buildings, transit hubs, and sporting events. Law enforcement agencies also urged the public via Twitter and Facebook to report suspicious activity to the police.
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 such as the Empire State building, Rockefeller Center, St. Patrick’s Cathedral, the United Nations, and the World Trade Center site were being especially monitored.
Mayor Michael Bloomberg said the police department was fully prepared to protect the city.
‘‘Some of the security steps we are taking may be noticeable,’’ Bloomberg said. ‘‘And others will not be.’’
Security was also tightened at sports venues nationwide, though most events were held as planned. The postponement of Monday’s NHL game between the Bruins and Senators, and the cancellation of Tuesday’s NBA game between the Celtics and Pacers — both at TD Garden — were the most tangible reactions by sports officials to the explosions.
Still, jittery officials announced plans for security reviews of upcoming marathons and road races in cities large and small, including this weekend’s marathon in Lansing, Mich., Nashville’s Country Music Marathon on April 27, next month’s Indianapolis 500 Festival Mini-Marathon, and the San Francisco Marathon in June.
Race officials for the Illinois Marathon in Champaign and Urbana, Ill., 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.
‘‘I took a call from a very irate parent who screamed at me because I won’t cancel the race, because I'm putting her daughter at risk,’’ said Jan Seeley, a director for the Illinois Marathon. ‘‘And we’re anticipating more of that.’’
The London race’s chief executive, Nick Bitel, said marathon officials contacted the police to discuss security plans ‘‘as soon as we heard the news’’ about Boston. He expressed shock and sadness about the situation in Boston, saying, ‘‘It is a very sad day for athletics and for our friends in marathon running.’’
Sunday’s marathon in Lansing, Mich., will have stepped up security. Police Chief Teresa Szymanski said people attending the marathon will be protected. She says there will be additional patrols and bomb sweeps.
And the explosions will prompt Indianapolis 500 officials to take another look at how to make this year’s race safer.
An estimated 250,000 fans attend the race each year, and unlike most sporting events, fans are permitted to bring their own food, drinks and coolers to the track on race day. A year ago, track officials reduced the permissible size of coolers fans could bring to the race.
While speedway spokesman Doug Boles says track officials have already started discussing safety measures for this year’s race, Monday’s bombing is likely to create a new round of dialogue. The race is scheduled to be run May 26.