About 300 protestors at the Books Not Bombs rally were penned into Town Hall Square by more than 200 police, who warned demonstrators they would be arrested if they attempted to break the cordon and stage a street march.

Carrying placards declaring "Arab voices will not be silenced" and "no blood for oil", most protestors satisfied themselves with chanting anti-war slogans.

However, police said there were three arrests and one undercover officer was forced to use capsicum spray to defend himself when he was pinned against a wall by a group of young men.

Another small group caused minor damage at the nearby Darling Harbour tourist area after the main demonstration broke up, throwing cafe chairs into the water and knocking over shop displays over.

The violence did not approach the levels of last week's protest, which ended with 33 youths arrested and four police injured after they were pelted with chairs, bottles and marbles.

Organisers said they were determined to stage a peaceful protest and at one point marshalls linked hands and stood in the path of a group of about 50 adolescent males, some wearing headscarves and facemasks, to prevent them confronting police.

A small number of plastic bottles were aimed at police but fell short of their target and hit the marshalls, who wore stickers identifying themselves as "legal observer", "parents for peace" and even "aunties for peace" -- sporting hair rollers and aprons.

Mohamad al-Wadee, 16, of Merrylands, said there was anger among Australian youths, particularly those with relatives in the Middle East, at Prime Minister John Howard's decision to join the United States and Britain in invading Iraq.

"We want the troops to come back and stop killing our people," al-Wadee said, only his eyes visible behind black and white face scarves.

Asked about his attire, al-Wadee replied: "Everyone is saying people who wear this are terrorists, I want to show they're not."

SPACE.WIRE