SAN FRANCISCO - For a second consecutive day, thousands of protesters flowed through the streets of several cities Sunday to call for an end to the funding of the Iraq war or the immediate return of US troops.

Wearing his original uniform and a Purple Heart medal, Harold Unsicker, 88, joins thousands of anti-war demonstrators gathered in San Francisco on Sunday, March 18, 2007. [AP]

Demonstrators converged in San Francisco, New York, Portland, Ore., and elsewhere to mark the fourth anniversary of the US invasion of Iraq and call on President Bush to heed what they said was the will of the people.

In largely peaceful demonstrations, about 3,000 people in San Francisco closed Market Street, a major downtown thoroughfare; in New York, more than 1,000 protesters converged in a park near the United Nations headquarters.

Dozens of police in San Francisco on foot and motorcycle blocked traffic and kept an eye on the crowd, which stretched for blocks through the financial district. No arrests were reported by late Sunday afternoon.

Gary Fong, 65, carried a sign calling on President Bush to "listen to America" as he marched in San Francisco.

"I think the war effort at this point is futile," the retired school guidance counselor and former Army intelligence officer said. "We want to do our part to express to Bush and the government that change needs to be made."

In New York, where union members, representatives of the Rev. Jesse Jackson's Rainbow-PUSH Coalition and war veterans joined protesters, the procession stretched for several blocks.

Actor Tim Robbins, speaking at an earlier rally organized by the New York chapter of United for Peace and Justice, told the crowd that getting Congress to cut off funds for the war "would be a good way" to get the troops home.

"The American people want this war to end," said Robbins, a frequent anti-war protest participant. "That's the message they sent last November in the election. When are we going to start listening to them?"

Police lined sidewalks, and some walked ahead of the protesters as they marched toward the offices of Sens. Charles Schumer and Hillary Rodham Clinton. Demonstrators carried signs reading "Impeach Bush," and "Not one more dollar, not one more death."

In Portland, Ore., thousands of marchers packed a grassy stretch downtown to call for an end to the war.

"There are Iraqis who can rebuild their country," said Raed Jarrar, an Iraqi-Palestinian blogger, told the crowd. "They don't need someone to come from thousands of miles away to tell them how to treat their neighbor. They are the only ones who can end this violence."

At the end of the march, a small group of protesters left the route and continued walking. Police followed them, and then a scuffle ensued, with police using pepper spray. At least two people were detained.

President Bush was at Camp David in Maryland for the weekend. Spokesman Blair Jones said of the protests: "Our Constitution guarantees the right to peacefully express one's views. The men and women in our military are fighting to bring the people of Iraq the same rights and freedoms."

This week, the House plans to vote on a war spending bill that includes a troop withdrawal deadline of Sept. 1, 2008. That timeline would speed up if the Iraqi government cannot meet its own benchmarks for providing security, allocating oil revenues and taking other essential steps. Bush has threatened a veto.

The San Francisco march appeared to comprise at least 3,000 people; in New York, it appeared to be well over 1,000 people.

Trish Gorman, who rode a bus with 55 other people from Bennington, Vt., said: "The people have to speak. The government is not listening to the people. Sitting quietly at home is not doing it."

She said she supported a "safe and well-thought-out defunding and withdrawal" from Iraq.

War protester Michelle Barish said she had sent a gas mask to her brother, a soldier soon to be deployed to Iraq, but was concerned that cutting funds was not the right way to bring the war to an end.

"If they cut off funding, does that mean I'm going to have to send a bulletproof vest and care packages?" she asked.

No counter-demonstrators were visibly present in New York, as they had been at an anti-war rally in Washington on Saturday that drew thousands to the Pentagon and the Lincoln Memorial.

In San Francisco, a smattering of counter-protesters waving American flags also gathered in what they described as a show of support for US troops.

"It's important to make sure that the sacrifices that we've already made are worth it," said Leigh Wolf, 20, a San Francisco State University student. "This is a war we can still win."