Seattle police say the level of open violence toward officers at Monday's Occupy the Port protest hasn't been seen since the World Trade Organization was here in 1999.

"It's been a long time since we've seen people throwing things that could kill people, not since WTO," said Asst. Chief Mike Sanford at a news conference Thursday. "We've seen debris thrown, but ... not bricks, not sharpened rebar, not things that would kill somebody."

Sanford spoke while airing a five-minute video shot by civilian employees of the Police Department during Monday's protest, which was part of an effort to shut down ports along the West Coast.

Some demonstrators complained that police were unnecessarily forceful, or even brutal, in their efforts to clear the street.

The Rev. John Helmiere, of Valley and Mountain Fellowship in Southeast Seattle, filed a complaint with the department alleging that officers struck him several times in the head outside Terminal 18 on Harbor Island. He was not hospitalized.

He described the episode in an essay published in local blogs.

"An officer pulled me down from behind and threw me to the asphalt. Between my cries of pain and shouts of 'I'm a man of peace!' he pressed a knee to my spine and immobilized my arms behind my back, crushing me against the ground."

Helmiere says he joined the Occupy march to support short-haul truckers, contract laborers who work without benefits to earn about $30,000. They are, according to Helmiere, "some of the most underpaid and exploited laborers in our city."

The 5 p.m. melee in which Helmiere claimed to be assaulted happened near the Terminal 18 entrances where Sanford said a group of people who were "bent on being violent" had cut through a fence and built a barricade in the road of wood, metal and debris.

When police moved to clear the street, someone in the crowd of demonstrators tossed a lit flare at them, and police then rushed to seize people. The police video shows items identified by Sanford as bricks flying through the air and paper bags filled with paint littering the ground.

Sanford said flares, smoke grenades and sticks also were thrown at police.

He said police released "blast balls," concussive devises, into the crowd.

In all, 11 people were arrested on investigation of failure to disperse, assaulting an officer and obstruction, police said. Helmiere was among them.

The protesters at the barricade on Klickitat Avenue Southwest were a splinter group of a larger demonstration that drew between 500 to 700 people to the Port terminals, according to police estimates of the crowd.

Helmiere said he was beaten after locking arms with fellow protesters, a tactic that Sanford described as dangerous because it makes it more difficult for police to isolate and arrest a single individual.

Seattle police said the video released Thursday was culled from 45 minutes of video shot at the event.

Sanford, who said he watched the melee unfold in front of him, said he was "surprised at the level of violence." He said there's a "difference between peaceful picketing ... and violent, illegal picketing."

For officers standing the line, "it's scary and it's dangerous" to see objects thrown at you from the crowd, he said.

He said that the Occupy movement, which began in New York as a protest against what was seen as immoral tactics used by Wall Street to gain wealth, have been primarily peaceful.

Sanford suggested that demonstrators who want to protect the purity of the movement's message may want to help police identify those who threw objects at officers.

"Help us identify those people," he said. "That is not the message that Occupy Seattle wants to get out."

Staff reporter Mike Lindblom contributed to this report.

Christine Clarridge: 206-464-8983 or cclarridge@seattletimes.com