Sixteen Afghans have been killed and more than 100 hurt since Wednesday in the worst anti-US protests across Afghanistan since US forces invaded in 2001 to oust the Taliban for harbouring Osama bin Laden and his al-Qaeda network.

Newsweek magazine said in its May 9 edition investigators probing abuses at the U.S. military prison at Guantanamo Bay found that interrogators "had placed Quran on toilets, and in at least one case flushed a holy book down the toilet."

Muslims consider the Quranthe literal word of God and treat each book with deep reverence.

"If proven that this happened, then we will strongly ask the American government to put on trial and punish whoever is the culprit," Karzai told a news conference. Such sacrilege was unacceptable to every Muslim.

The United States has tried to calm global Muslim outrage over the incident, saying disrespect for the Quran was abhorrent and would not be tolerated, and military authorities were investigating the allegation.

International Muslim groups in Saudi Arabia also called on the United States to investigate and punish those responsible.

The 57-nation Organisation of the Islamic Conference said the report had enraged hundreds of millions of Muslims and would "provide fanatics and extremists with excuses to ... justify their acts of violence and terrorism."