WASHINGTON (Reuters) - Marijuana smoke-ins, street parties and concerts marked the informal 4/20 pot holiday across the country on Thursday, but police spoiled one cannabis event near the U.S. Capitol with arrests and seizure of joints.

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To boos from onlookers, U.S. Capitol police led away pot activists who distributed joints to congressional staffers and others as part of a campaign to generate support for marijuana law reform in Congress.

The police action in Washington on the day of celebration for marijuana fans underscored the drug’s legal limbo in much of the United States. More than two dozen states have legalized pot for medical or recreational use, but it remains unlawful under federal statutes.

A Quinnipiac University poll released on Thursday showed U.S. voters back legalization by a margin of 60 percent to 34 percent, the highest level of support for legalized pot ever recorded by the survey.

The arrests in Washington surprised organizer Adam Eidinger, who said the event was held on a District of Columbia sidewalk across the street from the Capitol to avoid conflicting with federal law. Marijuana possession is legal in the District.

He and others planned to protest for marijuana reforms on Monday by lighting up on the Capitol grounds.

“A lot of people are never exposed to this,” a 22-year-old Senate staffer who declined to give his name said after being handed two joints. “It should be considered more.”

According to the marijuana magazine High Times, the concept of 4/20 originated in the early 1970s with teenagers in San Rafael, California, who used it as a code for the time in the afternoon they would gather to smoke the plant.

The Oxford English Dictionary added “420” as a noun last month, saying it was American slang referring to marijuana or the action of smoking it.

In California, where voters made recreational marijuana use legal last year, San Francisco on Thursday will hold its first permitted 4/20 celebration at the event’s traditional “Hippie Hill” site in Golden Gate Park.

Downtown Denver planned a pro-pot rally featuring a free concert by rapper 2 Chainz.

In Wyoming, Minnesota, police posted a gag picture on their Twitter feed of an officer poised with a net near snacks that might attract hungry 4/20 celebrants.

“Undercover #420 operations are in place. Discreet traps have been set up through the city today,” the post said.