Protesters angry over American demands that South Korea pay more for defense destroyed portraits of the U.S. ambassador stuck on blocks of tofu outside the U.S. embassy on Friday after police warned them against staging a more aggressive demonstration.

U.S. Ambassador Harry Harris has become a political lightning rod for South Koreans angered by U.S. President Donald Trump's push to get South Korea to pay billions of dollars more toward maintaining the 28,500 American troops stationed there.

"Harris out! We are not a U.S. colony! We are not an ATM machine!" the demonstrators chanted outside the embassy, surrounded by phalanxes of police.

The left-leaning protesters from several youth groups cheered as two students smashed up blocks of tofu and acorn jelly adorned with paper portraits of Harris.

Longtime allies, the United States and South Korea are in dispute over how much each should pay for the U.S. troops in South Korea. Trump has demanded Seoul pay as much as four billion U.S. dollars more a year, according to South Korean officials, and a new round of talks is scheduled in Seoul next week.

South Korea currently contributes about 900 million U.S. dollars to the upkeep of U.S. troops in the country.

"How is it possible for a tenant to ask for five-fold increase in rent from its landlord?" Kwon Oh-min, a Youth Party representative, said outside the U.S. embassy on Friday.

South Korea has the third-largest presence of U.S. troops based overseas after Japan and Germany. Major bases include the U.S. Army Garrison Humphreys in Pyeongtaek, south of Seoul, which covers 14.7 million square meters.

In October, dozens of progressive university students climbed into the grounds of the ambassador's residence in protest against the U.S. presence in the country, sparking calls from the embassy for more police protection.

Another gathering of progressive groups is planned for Saturday outside the U.S. embassy to urge Washington to withdraw its request for defense cost-sharing increases ahead of the next round of the Special Measures Agreement (SMA) talks next week.