Cities, venues put on alert

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.

Police in Los Angeles, Washington, San Diego, Las Vegas, Detroit, Atlanta and other major cities were monitoring events closely and assessing increases in security measures.

The Nevada Department of Public Safety said Monday it will continue to be proactive with security and enforcement strategies. As a precautionary measure, it is collaborating with federal officials to monitor and implement additional safety efforts in the wake of the Boston bomb attacks.

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 — after the bombs n Boston.

Across the U.S., 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 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.

In California, emergency management officials activated their statewide threat assessment system, which was established after the Sept. 11 attacks .