South Korean police detained 19 students on Friday after several climbed over the wall into the grounds of the US ambassador's residence in Seoul in protest against the US troop presence in the country.
The group, which identifies itself as a coalition of progressive university students, posted photos on its Facebook account in which several members used ladders to climb over a wall surrounding the home of Ambassador Harry Harris.
In a separate video, apparently broadcast from inside the compound, they accused the United States of demanding a 500% increase in the cost of keeping some 28,500 troops in South Korea, holding a banner saying "Leave this soil, Harris".
"Stop interfering with our domestic affairs," they shouted, followed by other chants "Get out", and "We don't need US troops", before being marched out of the residence by police.
Approximately 20 Korean nationals illegally entered the official residential compound of the US Ambassador and attempted to forcibly enter the residence itself, said William Coleman, spokesman for the US Embassy in Seoul said in a statement on Saturday.
This is the second instance of illegal entry into the Ambassador's residential compound in 14 months.
"We are seriously concerned about the illegal breach of the Ambassador's residential compound and urge the ROK to protect all diplomatic missions and residences," Coleman said, using the acronym for South Korea's official name, Republic of Korea.
South Korea's foreign ministry said it had requested increased security for the US embassy and the ambassador's residence.
"Any harm or attack on such a diplomatic mission cannot be justified under any circumstances, and the government will take all appropriate measures to protect the missions and prevent any acts that disturb their wellbeing," the ministry said in a statement.
A police official told Reuters that 19 students were taken to a police station for questioning.
In June, the student group held a forum to present their "research findings" on the achievements of North Korean leader Kim Jong Un, lauding him as a caring and influential leader.
The students also attempted to break into the US Embassy in Seoul last January before being stopped by police.
The two countries are currently in talks over how to share the expense of keeping the US troops who guard against the threat from nuclear-armed North Korea, a legacy of the 1950-53 Korean War.
A fresh round of talks will be held in Hawaii on Oct. 23-24 to negotiate a deal that will replace one due to expire at the end of this year, the foreign ministry said.
"Our government will have close discussions under our basic stance that we will have a fair, reasonable share of the costs," the ministry said in a separate statement on Friday.
"We expect the talks will take place in a way that reinforces the alliance and joint defence posture."