PORTLAND, Ore. — Anti-Wall Street protesters in Portland headed for a police showdown over orders to abandon a city park encampment and authorities elsewhere stepped up pressure against the demonstrators, arresting nearly two dozen.

Tensions were increasing early Sunday in Portland, where as many as 200 protesters ignored a midnight deadline to abandon an encampment or face possible arrest.

Occupy Portland protesters dismantled large sections of their encampment amid a heavy police presence on Saturday, but dozens of tents remained after midnight.

Mayor Sam Adams ordered the camp shut down, citing unhealthy conditions and the encampment's attraction of drug users and thieves. Paramedics treated two people suffering from apparent drug overdoses, one on Friday and one on Saturday, bringing to four the number of nonfatal overdoses inside the camp, police said.

Demonstrators rallied Saturday evening as organizers said they hope radical elements don't use violence to overshadow the movement's message of peaceful resistance to income inequality and what they see as corporate greed.

But police prepared for a possible clash, warning that dozens of anarchists may be planning a confrontation with authorities. Officers seized pieces of cement blocks Friday, saying they were told some demonstrators had plans to use them as weapons against police. They said they believe some demonstrators are building shields and trying to collect gas masks.

For the second time in as many days, Oakland city officials warned protesters Saturday that they do not have the right to camp in the plaza in front of City Hall and face immediate arrest.

The eviction notices come as officials across the country urged an end to similar gatherings in the wake of three deaths in different cities, including two by gunfire.

In Salt Lake City, police arrested 19 people Saturday when protesters refused to leave a park a day after a man was found dead inside his tent at the encampment.

The arrests came after police moved into the park early in the evening where protesters had been ordered to leave by the end of the day. About 150 people had been living in the camp there for weeks.

City officials rescinded permits for the group to stay in the parks overnight Friday, after a man was found dead inside a tent at the Occupy Salt Lake City encampment, from what police said was a combination of drug use and carbon monoxide.

Authorities in Denver forced protesters to leave a downtown encampment and arrested four people for interfering with officers who removed illegally pitched tents, said police spokesman Sonny Jackson.

Jackson said police had advised protesters since Wednesday that their tents in Civic Center Park and on a nearby sidewalk were illegal.

Protesters have been marching in Denver for sixth straight Saturdays — with dwindling numbers.

Violence marked the protest in San Francisco Saturday where police said two demonstrators attacked two police officers in separate incidents during a march.

Police spokesman Carlos Manfredi said a protester slashed an officer's hand with a pen knife while another protester shoved an officer, causing facial cuts. He said neither officer was seriously hurt, and the assailants couldn't be located.

Demands for Oakland protesters to pack up increased after a man was shot and killed Thursday near the encampment site.

"Your activities are injurious to health, obstruct the free use of property, interfering with the comfortable enjoyment of (Frank Ogawa Plaza), and unlawfully obstruct the free passage or use of a public park or square," the notice read.

Police and a city official did not respond to requests for comment on whether police were preparing to forcibly clear the camp. Protesters said Saturday's peaceful march and rally in front of City Hall was a show of solidarity with activists in Egypt.

Oakland officials first issued the eviction notice Friday after first pleading with protesters to leave the encampment.

Police officials have said a preliminary investigation suggested the shooting resulted from a fight between two groups of men at or near the encampment. Investigators do not know if the men in the fight were associated with Occupy Oakland, but protesters said there was no connection between the shooting and the camp.

The victim has not been identified.

The shooting occurred the same day a 35-year-old military veteran apparently committed suicide in a tent at a Burlington, Vt., Occupy encampment. Police said a preliminary investigation showed the veteran fatally shot himself in the head. They said the death raised questions about whether the protest would be allowed to continue.

Meanwhile, in Southern California a small group of protesters braved soggy weather on Saturday to gather for the first time under the banner of Occupy Inland Empire. Members of Occupy movements in Fontana, Redlands, Riverside, and other nearby towns marched past banks and in front of San Bernardino City Hall in what they called a "visibility action," The Sun newspaper reported.

Protesters inspired by the Occupy movement also planned to camp over the weekend in Hendy Woods State Park in Mendocino County. The park is currently closed to camping, but about 150 to 200 people pitched tents Saturday.

The protesters want the state to keep the park open next year. It is currently among 70 state parks slated to close under state budget cuts.

"This is really devastating to a lot of local people, a lot of local businesses," organizer Cyd Bernstein said.

Associated Press writers Terry Collins in Oakland, Josh Loftin in Salt Lake City, Jim Anderson in Denver and Andrew Dalton in Los Angeles contributed to this report.