Notorious activist 'banned from G20' by police

A Brisbane activist who was once jailed in the US for helping disable a war plane says he has been banned from the G20.

Ciaron O'Reilly said police served him a notice today saying he was prohibited from entry into all G20 security areas until Monday.

Mr O'Reilly was on the street in West End in inner Brisbane holding a Free Julian Assange poster when police served him with the letter.

The incident was witnessed by photographer James Nelson.

"They were obviously looking for him. They have obviously nailed him as someone they don't want in the area," Mr Nelson told AAP.

The letter is signed by Queensland Police Commissioner Ian Stewart.

It says Mr Stewart has been been provided with information about Mr O'Reilly and the commissioner "is reasonably satisfied that you are a person who should be included on the prohibited persons list."

The seasoned activist once served 13 months in prison in the US for his involvement in disabling a B-52 bomber during the 1991 Gulf War.