Afghan students burned an American flag and shouted slogans against the US military on Thursday, as protests at reported abuse of Islam's holy book at the US jail in Guantanamo Bay spread to the capital and into Pakistan.

Protesters also attacked a government outpost and the offices of two international relief organizations to the south of Kabul, injuring one aid worker and leaving a trail of destruction, an aid worker and an official said.

The unrest came a day after riots in an eastern city left four people dead in the worst anti-American protests in Afghanistan since the fall of the Taliban in 2001.

America's war on terror

While most of the protesters appeared to be students, officials have suggested that elements opposed to the country's US-backed re-emergence were stirring the violence, which has also targeted the United Nations and American troops.

"It's the symbols of this change in Afghanistan that have been singled out," said Paul Barker, director of CARE International, one of the largest international relief groups in Afghanistan. "There are probably people around the country inciting this."

Barker said a group of high school students assailed the CARE office in Mohammed Agha district of Logar province on Thursday morning, beating one staff member and destroying equipment. The office of another foreign relief group next door was set on fire.

Logar Gov. Amanullah Hamimi said protesters also broke the windows of the local government office and that unidentified men had destroyed a nearby mobile phone mast with rockets during the night.

In Kabul, more than 200 young men marched from a dormitory block near the university chanting "Death to America!" and carrying banners including one stating: "Those who insult the Quran should be brought to justice."

At the entrance to the university, a man with a clipped beard and spectacles read a resolution calling on President Bush to apologize and opposing long-term U.S. military bases in Afghanistan.

About two dozen students clambered onto the roof of a nearby building and burned an American flag to applause and cries of "God is great!" from the crowd below. Dozens of police looked on.