Thousands of antiwar demonstrators clashed with riot police in the Egyptian capital today, throwing stones at the U.S. Embassy and waving Iraqi flags as they demanded an end to U.S. military action in the Persian Gulf region.

After protesters attempted to move within 50 yards of the heavily fortified embassy, police unleashed dogs and fired water cannons, sending the crowds running through downtown streets. Ambulances rushed to help bloodied protesters after they were beaten by baton-wielding police.

"The U.S. wants to try all its new weapons on the Arabs so we must speak louder," said Ahmed Shehat, a college student who had been chanting: "Our blood is not cheap," and "Please arm us and send us to Baghdad."

"If Saddam Hussein, and George Bush fight man to man," he said, "Bush will die."

The protest in Cairo was in contrast to milder demonstrations in other Arab countries, where public anger was muted by heavy government security.

In Saudi Arabia and Jordan, thousands of police officers in riot gear guarded the streets as protesters complained not only about the U.S. attack on Iraq but also about their own leaders allowing thousands of U.S. troops to use their airspace and bases.

In Saudi Arabia, the government has gone to great lengths to veil the presence of more than 5,000 U.S. troops at two air bases in the desert, one of which, Prince Sultan air base, is being used to direct U.S. air operations. Hours after the start of hostilities, the Saudi foreign minister, Prince Saud Faisal, reiterated his government's position that it was not taking part in a war against "brotherly" Iraq. In a statement to the official Saudi Press Agency, Saud expressed "grave concern and deep regret" over the war. He said he hopes "military operations end as soon as possible and that there be a return to the language of peace efforts."

In Syria and Libya, thousands of protesters called for U.S. ambassadors to leave their countries.

In Beirut, thousands gathered in front of the British embassy and the local headquarters of the United Nations. The groups included students from Beirut's American University and Arab University, along with Greenpeace activists and Palestinian refugees.

"It is a pity, a pity, a pity, a pity and a shame," said Angham Saleh, 21, a business student at the American University. "We feel so helpless. We feel handcuffed."

Scattered demonstrations were staged in the Palestinian territories in support of Iraqi President Saddam Hussein and against the U.S. attack on Iraq. In the West Bank city of Ramallah, several hundred protestors gathered in the streets. In Bethlehem, demonstrators waved Iraqi and Palestinian flags and carried portraits of Hussein.

In Gaza City, about 100 protesters fired rifles into the air and paraded through the streets. The Palestinian Authority canceled classes today for all schoolchildren.

The Egyptian protest was organized by the Muslim Brotherhood, the country's largest Islamic political party, and other opposition groups. The Muslim Brotherhood has renounced violence, but its leaders said they were furious about the war in Iraq and felt helpless to defend the Iraqi people.

"American interests shouldn't feel safe in the Arab region," said Essam el-Eryan, a prominent Muslim Brotherhood member who organized the protest. "Iraq should be supported to transform the swift war that the U.S. wants, to gang and city fights, to make Iraq a graveyard to the Americans. This way, American people will revolt against this war."

One group of protesters tried to hush the crowd as security forces, including uniformed police officers and soldiers, and men in dark sunglasses and suits and carrying walkie-talkies approached. Protests are rarely allowed in Egypt, where political opposition parties, including the Muslim Brotherhood, are officially banned.

The police succeeded in dispersing larger protests, breaking the demonstrators into smaller pockets. In the afternoon, however, about 5,000 people regrouped in downtown Cairo's famed Tahrir Square. The protesters threw stones and police advanced, spraying them with jets of blue-dyed water.

The demonstrators were varied in appearance -- there were society women who wore black, families from villages outside of Cairo, and Arab Americans here on study programs.

"I feel sick, this is genocide," said Ferial Ghazoul, an Iraqi professor of comparative literature at American University who has lived in Egypt since 1979. She said she was worried about her relatives and other fellow Iraqis.

"The only one who can save us now is God," said Gamil Rabie, 45, who held up a copy of the Koran to the clear and sunny sky.

"This protest is the minimum we could do," said Sahar Abdelraeof, 28, who took off from her job at a sugar factory and got a babysitter for her two children so she could join the antiwar protest.

At one point, a small crowd of Americans, French and Canadians also gathered in the square and called for Bush to be removed from office.

"I get into a cab and the driver asks if I am American," said Reema Hijazi, 19, of Chantilly, Va., who is studying here for a semester. She has one Palestinian and one American parent. "I say 'I am' and then I say, 'I am very sorry.' "

Staff writer Carol Morello in Riyadh, Saudi Arabia, correspondent Molly Moore in Jerusalem and special correspondent Alia Ibrahim in Beirut contributed to this report.

The Beach refugee camp in Gaza was one of many places in the Middle East where protests erupted East against the war in Iraq. Many carried signs in support of Saddam Hussein.