Thousands of antiwar protesters have taken to the streets in many Arab cities around the world.

In the Yemeni capital Sanaa, an 11-year-old boy and a policeman were shot dead in a clash between police and protesters, security sources said.

At least 10 people, including three policemen, were also hurt in the shoot-out that erupted after police blocked about 3,000 protesters from marching on the US embassy.

Witnesses said the demonstrators set tyres and garbage cans alight while chanting: "Oh youth of Islam, say no to war and yes to peace" and "No to US hegemony and hypocrisy".

In Cairo, the biggest city in the Arab world with almost 17 million people, at least 5,000 angry protesters clashed with police using water cannons outside the historic al-Azhar mosque.

"With our heart and our soul, we sacrifice ourselves for Iraq," chanted demonstrators outside al-Azhar, and in the Palestinian cities of Gaza and Nablus.

Protesters set a truck alight which they said was spraying them with water as others called for "jihad" (holy war) against the US and British "infidels" and in support of the Iraqi people.

In a rare statement, Egypt's interior ministry appealed to citizens to vent their frustration in an orderly manner through previously authorised demonstrations.

In Jordan, thousands of protesters fought baton-wielding riot police after the authorities sealed off parts of the capital, Amman, to foil Islamist organised pro-Iraq protests.

Police in the Lebanese capital Beirut used tear gas and water cannon to hold back hundreds of stone-throwing youths - many also shouting "death to America" - who tried to march towards the US mission.

Hundreds of protesters in Bahrain, the headquarters of the US Fifth Fleet, also took to the streets to show their fury.