Police shot four protesters to death Wednesday to stop hundreds from marching on a southern U.S. military base, as Islamic organizations called for an end to deadly rioting across the Muslim world over drawings of the Prophet Muhammad.

An Afghan protester shouts slogans as he marches through the streets of Kabul during a demonstration in Kabul, Afghanistan, Wednesday, Feb. 8, 2006. Afghanistan's top Islamic organization on Wednesday called for an end to violent protests against drawings of the Prophet Muhammad, as police shot dead two protesters to stop an angry crowd from marching on a U.S. military base in the southern part of the country. [AP]

"Islam says it's all right to demonstrate but not to resort to violence. This must stop," said senior cleric Mohammed Usman, a member of the Ulama Council — Afghanistan's top Islamic organization. "We condemn the cartoons but this does not justify violence. These rioters are defaming the name of Islam."

Other members of the council went on radio and television Wednesday to appeal for calm. It followed a statement released Tuesday by the United Nations, European Union and the world's largest Islamic group urging an end to violence.

"Aggression against life and property can only damage the image of a peaceful Islam," said the statement released by Ekmeleddin Ihsanoglu of the Organization of the Islamic Conference, U.N. Secretary-General Kofi Annan and the EU chief Javier Solana.

Meanwhile, a U.S. military spokesman said the United States and other countries are examining whether extremist groups may be inciting protesters to riot around the world because of the cartoons that have been printed in numerous European papers.

"The United States and other countries are providing assistance in any manner that they can ... to see if this is something larger than just a small demonstration," Col. James Yonts told reporters when asked whether al-Qaida and the Taliban may have been involved in days of violent demonstrations in Afghanistan.

The Afghan protests have involved armed men and have been directed at foreign and Afghan government targets — fueling the suspicions there's more behind the unrest than religious sensitivities. But Yonts stressed they had no evidence to support suggestions that al-Qaida or Taliban are linked to the riots in Afghanistan.

Hundreds rioted outside the U.S. military base in the southern city of Qalat on Wednesday, throwing rocks at Afghan police. Police tried to clear the crowd by firing shots in the air, then were forced to fire into the crowd, said Ghulam Nabi Malakhail, the provincial police chief.

Four people were killed and at least 20 were wounded, he said.

The protesters then set fire to three fuel tankers that were waiting to deliver gas to the base, Malakhail said. He said U.S. troops fired warning shots into the air.

A U.S. military spokesman, Lt. Mike Cody, said he had no details on the incident.

Eleven people have been killed in the past week as thousands have taken to the streets in a dozen Afghan cities and towns to march against the cartoons, which have been reprinted in various European media after first appearing in a Danish newspaper in September.

The drawings — including one depicting the prophet wearing a turban shaped as a bomb — have touched a raw nerve among Muslims. Islam is interpreted to forbid any illustrations of Muhammad for fear they could lead to idolatry.

The caricatures were first published in the Danish newspaper Jyllands-Posten. Culture editor Flemming Rose told CNN on Wednesday he came up with the idea after several local cases of self-censorship involving people fearing reprisals from Muslims.

"There was a story out there and we had to cover it," Rose said. "We just chose to cover it in a different way, according to the principal: don't tell it, show it."

Rose also said his paper was trying to contact a prominent Iranian newspaper that said it would hold a competition for cartoons on the Holocaust to test whether the West extends the principle of freedom of expression to the Nazi genocide as it did to the Muhammad caricatures.

Rose said Jyllands-Posten wants to publish those cartoons on the same day the Iranian paper Hamshahri does.

Elsewhere, about 300 Palestinians attacked an international observer mission in the West Bank city of Hebron and tried to set one of the buildings on fire in a protest against the cartoons.

Sixty members of the mission were inside at the time, said Gunhild Forselv, a spokeswoman for the Temporary International Presence in Hebron, or TIPH, which serves as a buffer between Israeli settlers and Palestinians in the volatile city.

Eleven Danish members of TIPH left more than a week ago after protests against the cartoons began sweeping across the Muslim world, Forselv said.

The protesters chased away outnumbered Palestinian police stationed outside the mission, Forselv said. Reinforcements were called in to quell the disturbance.