Police stepped up security around the US embassy here and other American installations across the country following anti-US protests that saw radicals breaking into a US military base and firebombing another facility in recent days.
Early Thursday, two Molotov cocktails were thrown over the wall of Camp Page in the eastern city of Chuncheon, local police told AFP by telephone.
"The two Molotov cocktails landed on the ground inside the high wall but they caused little damage. Nobody was hurt," a police officer said.
"Two other Motolov cocktails fell on the flower bed outside the wall and we retrieved the burning debris. When we got there, the attackers had already gone."
Yonhap news agency said the Molotov cocktails were believed to have been thrown by student radicals who were driving past the base.
On Monday, some 20 students hurled 10 Molotov cocktails over the main gate of Camp Grey, a small US support post in southwestern Seoul. One student was arrested following the attack.
A day later, around 50 activists were arrested after breaking into a major US military base in northern surburbs of Seoul.
The attacks came after two US soldiers were cleared in court martials last week at Camp Casey, north of Seoul.
They were accused of negligent homicide in the deaths of 14-year-olds Shim Mi-Son and Shin Hyon-Sun, who were crushed to death in a road accident on June
General Leon LaPorte, commander of the 37,000 US troops in South Korea, indicated that the US forces would take measures to ensure safety of servicemen and their families against violent protests.
"As the commander of all the forces in Korea ... I have the reponsibility to ensure the safety of the service members and their families. I take that responsibility very seriously," LaPorte told journalists on Wednesday.
"If required, I will have to initiate some actions so that we could ensure that our service members and family members are not exposed to violence," he said.
He made the statement at a joint press conference with US Ambassador to Seoul Thomas Hubbard during which Hubbard conveyed words of apology from President George W. Bush over the deaths.
Activists want the two soldiers to go on trial in a Korean court. However under an accord between Washington and Seoul US troops stationed here under a mutual defense pact dating back to the 1950-1953 Korean War come under US jurisdiction for crimes committed while on duty.
The South Korean government asked for jurisdiction in this case but was denied by Washington.
Yonhap news agency said that since Tuesday 4,400 extra police had joined the 1,900 already guarding US installations here.