The demonstrators chanted anti-war slogans such as "The road to peace is U.S. out of the Middle East," "Trump says more war, we say no more," and "No justice, no peace; U.S. out of the Middle East" to express their anger and discontent over the U.S. military presence and action in the Gulf.

On Friday, a U.S. drone attack ordered by President Donald Trump killed Qassem Soleimani, commander of the Quds Force of Iran's Islamic Revolutionary Guards Corps, instantly inflaming the already strained Washington-Tehran tensions.

After the rally at the metro station, thousands of the protesters marched along Market and Mission streets in the downtown area to the UN Plaza north of City Hall, where several speakers delivered speeches in turn, accusing the federal government and U.S. military of conducting dangerous actions in the Middle East.

Richard Becker, West Coast coordinator of the U.S.-based civil rights group Act Now to Stop War and End Racism, also known as the ANSWER Coalition, told Xinhua that the U.S. air strike killing Soleimani was "an act of war" which would lead to an all-out war.

"I don't think that we could possibly understand that they would do such a thing such as an attack and not think that Iran would respond to it," he said.

"That can lead to a wider war, it can lead to an escalation, potentially into a full-scale war, a regional war, and it could even lead to a global war. So it's very dangerous," Becker said.

He added that the goal of Saturday's protest is to revive and build a new anti-war movement in the United States, citing a "very satisfactory turnout" of people who took to the streets to show "people's power."

"We have about 2,000 people here in San Francisco, and thousands and thousands of more people marched in other U.S. cities, including New York, Washington, Chicago, Los Angeles and many other places in the country," he said.

Gloria La Riva, an ANSWER organizer, told Xinhua that San Francisco locals came out on Saturday, along with people in more than 70 other U.S. cities to demand an end to the U.S. presence in the Middle East, and to oppose the U.S. "assassination" of Soleimani three days ago.

She slammed the Pentagon for its "very dangerous" attempts to destroy Iran, adding that "they've already destroyed Iraq in many ways, but they want to do away with Iran. Only people can stop the war and make this government bring the U.S. troops back home."

She rejected Trump's claim that the killing of Soleimani was aimed at eliminating a threat to U.S. security.

"It's a lie. Nobody with any logic can believe that because it was premeditated, unilateral, an act of aggression. It's a violation of all international law," she said.

She said the U.S. military action in Iraq and the Middle East would not bring any sense of security back home.

"People were very afraid, not afraid of Iran. They are afraid of the U.S. and afraid of Trump. We have to be here outside protesting. This is the only way to show the people of the country that they're not alone in their fear," La Riva added.

Ruthie Sakheim, a local teacher, criticized the Trump administration for killing a foreign military leader, which is "terrifying."

She blasted the federal government for abusing American tax payers' money for military purposes.

"We know that the weapons have been built up with all of our tax money that should be going to help the people in our country who are suffering from hunger and homelessness, and (they) don't have an education and don't have everything that they need," she said.

Saturday's protest was organized by the ANSWER Coalition, which also hosted a similar demonstration in San Jose in the South Bay Area on the same day.