WASHINGTON (Reuters) - Anarchist groups have threatened to shut down Republican Donald Trump’s swearing-in as U.S. president, but police in Washington said on Friday they believe the thousands of security officers assigned to the event will be able to head off any disruption. Dozens of activist groups plan to protest the Jan. 20 inauguration of the New York real estate developer, whose supporters are counting on him to fulfill a host of controversial campaign promises including building a wall on the Mexican border and deporting millions of illegal immigrants. Police expect some 900,000 people to flood Washington for the inauguration ceremony, which includes a parade from the U.S. Capitol to the White House along streets thronged with onlookers. Interim Police Chief Peter Newsham told reporters on Friday that in addition to the more than two dozen activist groups that have sought permits for peaceful demonstrations, Washington police were aware of anarchist groups vowing online to interrupt the proceedings. “The fact that you have some folks that are indicating on social media that they’re coming to shut down the inauguration events is something that we will be prepared for,” Newsham said. “We’ve experienced that type of thing before in the city and we’ll be able to handle it.” Asked about the prospect of mass arrests, Newsham said: “That’s one of the things that we have to prepare for, but we don’t anticipate that will be the case.” Protests are planned  before, during and after the inauguration, with the biggest event the Women’s March on Washington on Jan. 21. The National Park Service said Thursday it would start issuing permits for protest sites after civil rights lawyers threatened to sue, saying the agency was quashing dissent. About 3,000 police officers from outside the District, 5,000 National Guard troops and federal agents will staff buffer crowd-control barriers and bag checks, said Brian Ebert, the head of the Secret Service’s District field office. Barriers will be in place to prevent any possible truck attack, such as the attacks in Berlin last month and in Nice, France, in July. A pro-pot lobbying group has vowed to distribute 4,200 joints and light up near the inaugural site to show support for legalization of marijuana nationwide. Marijuana is legal in the District of Columbia but can only be consumed in private. Asked if police would bust smokers, Mayor Muriel Bowser said, “That wouldn’t be our first priority.” 