Six men suspected of involvement in violent protests outside the Israeli embassy in London against the Gaza offensive in January have been arrested in raids across the capital, police said on Tuesday.

The men, aged between 17 and 26, were detained on suspicion of violent disorder after demonstrations on January 3 and January 10 left 55 police officers injured and damaged shops and property.

One police officer was knocked unconscious after he was hit by a metal object during the second demonstration.

CCTV footage showed protesters hitting police with sticks and metal barriers, with one attack on police lines lasting three hours, police said.

The arrests were the first phase of a long-running operation to identify about 40 people thought to have been involved in the disturbances in Kensington, central London.

"Let me make it clear that those who corrupt and abuse the right to protest by using it as a guise to attack police and trash and loot shops cannot hide behind the crowds," said Chief Superintendent Ian Thomas in a statement.

"What happened during these demonstrations in January and what our officers and those shopkeepers were subjected to was not and cannot be described as lawful protest."

Police have arrested and bailed 62 people so far, including the latest arrests, and are looking for 24 more.