"President Bush, who has visited Korea and has a special feeling for the Korean people, has been touched by this tragedy," US ambassador Thomas Hubbard told a press conference.

"Just this morning, the president sent me a message asking me to convey his apologies to the families of the girls, to the government of the Republic of Korea and to the people of Korea.

"He asked me to express, and here I quote, his 'sadness and regret' over this tragic incident and to reiterate the United States' commitment to work closely with the Republic of Korea to help prevent such accidents from occurring in the future."

The South Korean government welcomed Bush's apology, Yonhap news agency said.

"It's a positive sign that President Bush expressed his sincere apology," the agency quoted a government official as saying.

It was unclear what effect the Bush apology would have on anti-US protests unfolding here. Some 1,000 students were gathering outside the main US military installation in Seoul as ambassador Hubbard was announcing the apology.

Activists said they were also preparing a cyber attack on the White House, the Pentagon and other US government departments.

Activists have staged regular protests outside US military installations since the deaths of 14-year-olds Shim Mi-Son and Shin Hyon-Sun on June 13, burning American flags and scuffling with riot police.

Unrest escalated after two soldiers accused of crushing the girls under the tracks of a 50-tonne vehicle were acquitted by a US military court last week.

The South Korea media said the trials were a sham and mainstream political leaders joined the radical left in calling for a revision of the status of the 37,000 US troops stationed in South Korea under a mutual defense pact dating back to the 1950-1953 Korean War.

North Korea denounced the trials as "illegal fraud", in a statement released by the official Korean Central News Agency citing the (North) Korean democratic lawyers association.

Hundreds of demonstrators rallied during the courts martial last week outside Camp Casey, a sprawling US military post near the border with North Korea, demanding the soldiers be tried by a South Korean court.

But under an accord between Washington and Seoul, US forces have legal jurisdiction over American troops committing crimes in South Korea while on duty. Seoul asked for jurisdiction in this case but was denied.

Many Koreans are genuinely bewildered that the soldiers walked free and that no one has been held legally responsible for the killings. Under the Korean criminal justice system they would almost certainly have been jailed.

General Leon LaPorte, commander of US forces in South Korea, said the accident served to underline differences in legal systems.

"That does not mean no one is responsible and we accept full responsibility for this tragic accident," he said at the press conference with Hubbard.

The South Korea cyber attack on Washington was being planned by a coalition of 130 South Korean civic groups, Yoo Yong-Jae, the coalition secretary general told AFP.

"South Korean Internet users are being asked to cram the servers with mail bombs," he said, adding however the timing of the cyber attack had not been decided and activists would get legal advice before the launch.

"We will launch the attack cautiously after studying legal aspects so that it should not be seen as cyber terrorism," he said.

Earlier Wednesday the two acquitted soldiers issued public apologies. Vehicle commander Sergeant Fernando Nino offered his "deepest and most heartfelt condolences" to the families of the girls while driver Mark Walker expressed "great remorse" over the deaths.

SPACE.WIRE