Protesters angry over American demands that South Korea pay more for defence 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.