WASHINGTON

Inauguration security operation switched on

Kevin Johnson
USA TODAY

WASHINGTON — Federal authorities flipped the switch Thursday on a far-reaching inaugural security operation aimed at thwarting a range of potential threats, from weaponized drones and vehicle attacks to active shooters and thousands of protesters.

Workers prepare the stage for the inauguration ceremony of President-elect Donald Trump on Jan. 19, 2017, in Washington.

Before dawn, a rolling series of street closures began forming a protective perimeter around the city where up to 900,000 people are expected for daylong ceremonies Friday marking the transfer of the government to the incoming administration of President-elect Donald Trump.

Perhaps underscoring the extent of the security preparations, authorities shut down the iconic Memorial Bridge early Thursday, a major artery linking the Lincoln Memorial and Arlington National Cemetery, across the Potomac River.

The Secret Service, which is overseeing the plan, said Thursday there were no specific or credible threats targeting the events. However, authorities are girding for an unusually large number of protesters. About 100 groups are expected, with more than 60 organizations preparing for Friday demonstrations. The largest of the Friday groups, the Answer Coalition, could bring up to 10,000 people to voice their opposition to war, police brutality and racism from a base near the inaugural parade route.

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The largest single group of demonstrators, up to 200,000, are expected to participate in the Women's March on Washington, a coalition of civil and human rights advocates scheduled to parade through Washington on Saturday.

The transformation of the capital from a normally open, walkable urban center to a city in semi-lockdown began taking shape earlier in the week with the strategic placement of concrete barriers, chain-link fencing and steel screens all along Pennsylvania Avenue. The entry to Trump's new namesake hotel, housed in the historic Old Post Office Pavilion, resembled an armed camp.

Security fences are set up in front of Trump International Hotel in Washington on Jan. 18, 2017.

At a recent security briefing, Homeland Security Secretary Jeh Johnson said authorities have taken special precautions against possible vehicle attacks, similar to those that killed 12 last month at a Berlin Christmas market and another that left 86 dead at a July Bastille Day celebration in Nice, France.

Johnson said heavy construction equipment, dumpsters and other physical barriers were being positioned around the city to restrict vehicle access to sensitive areas and assist with crowd control during three days of activities.

"The global terror environment is very different even from 2013,'' the secretary said, referring to the last inaugural ceremony marking President Obama's second term. "We have to be concerned about individual acts of violent extremism.''

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Counter-terrorism officials have been increasingly concerned in recent years of the recruitment campaign waged by the Islamic State terror group, whose operatives have been urging sympathizers in the United States, to lash out against domestic targets rather than risk travel to the battlefields in Syria and Iraq.

Overall, the D.C. security operation involves 28,000 officials, including 7,800 drawn from the ranks of the National Guard and about 3,000 law enforcement officers drawn from agencies across the country.

In addition to physical barriers the army of personnel, the city is literally strung with a network of cameras and other technology, including defenses against drones.

Johnson has declined to elaborate on the specific anti-drone measures, though those defenses have drawn the increasing attention of the Secret Service engaged in the in the daily protection of the White House complex.

In recent days, the Secret Service has been flooded with hundreds of inquiries from prospective visitors whose questions have run the gamut: Some have asked whether they can bring their own security equipment in the form of flak jackets, while others have wanted the agency to reserve space for their families along the parade route.

"There have been some odd requests,'' spokeswoman Cathy Milhoan said.

Stay with USA TODAY for full coverage of the 2017 inauguration.