Protest leader Renato Reyes said some activists were injured and at least 23 were arrested.
But as activists broke through a line of riot police and threw red paint and rocks, police responded with water spray from a fire hose, tear gas and batons.
The protesters were reportedly calling for an end to the presence of USA troops in the country while expressing their support to the independent foreign policy being initiated by President Rodrigo Duterte, according to the Philippine Daily Inquirer.
Manila Police Chief Oscar Albayalde insisted the driver was not to blame and said the protesters had been trying to flip the van.
The hardline president came to power in May and has since made a succession of anti-American outbursts, calling Barack Obama the "son of a whore" and telling the U.S. president to "go to hell".
On Friday, October 21, upon his expected arrival in Manila from his visit to China, Duterte said he plans to make an official announcement regarding the matter.
President Rodrigo Duterte has been bashing the U.S.in foul-mouthed tirades for weeks, stirring up anti-American sentiment in a country that has always been a staunch American ally.
"The PNP is now piecing together all facts and circumstances surrounding the violent confrontation between members of the Manila Police District and a group of militant activists in Ermita, Manila this morning", the PNP said in a statement released hours after the dispersal.
The protesters were calling for the removal of USA troops in the southern island of Mindanao.
"These acts of violence against legitimate protests clearly reveal the state's policy of terror against its people".
He told Mr Obama to "go to hell" and alluded to severing ties with Washington.
Anti-U.S. protesters outside the U.S. embassy in Manilla, Philippines, demanded American troops leave their country.
Another tweet claimed the protest was led by "national minorities" and perhaps did not follow the sentiment of the majority of the Philippine people.
The effort to engage China, months after a Hague ruling over South China Sea disputes in favour of the Philippines, marks a reversal in Philippine foreign policy since Duterte took office on June 30. He is also seeking to expand two-way trade and investments and financing for infrastructure projects.
Tension has been high between the Philippines and the United States since USA officials criticized Duterte's bloody war on drugs.
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