A German-Israeli artist who accused Twitter of failing to tackle anti-Semitic and racist hate speech has taken revenge by stenciling offending tweets outside the company's office in Hamburg.

A video posted on Monday (7 August) shows Shahak Shapira spray-painting messages like, "Germany needs a final solution to Islam", "Let's gas the Jews" and "N*****s are a plague to our society" on the ground next to the entrance to Twitter's building.

"If Twitter forces me to see these things, then they should have to see it as well," he said, claiming the tweets went against the company's guidelines.

The Berlin-based 29-year-old said he frequently sees tweets that "weren't just plain insults of jokes but absolutely serious threats of violence, homophobia, xenophobia or Holocaust denial".

He said he had reported about 300 tweets to Twitter over the last six months but only got nine responses – all of which said the tweets did not violate the social networking site's rules.

In comparison, Shapira said his complaints over 150 similar messages on Facebook led to 80% of them being removed by the company's administrators within three days.

A spokesman for Twitter told Reuters the company would not comment on the specifics of individual accounts for reasons of privacy, but said it strictly enforces its rules and had stepped up the policing of abuse on its network.

Twitter is now taking action on 10 times as many abusive accounts compared with the same time last year, the company added.

Shapira spray-painted 30 tweets in total outside the company's office, along with the message "Hey Twitter, delete this c**p."

"This will never be big enough to even visualise the amount of hate tweets on Twitter, but maybe we can at least give them some food for thought," he said.