An agreement on Tuesday by four major U.S. internet companies to block illegal hate speech from their European services shows the pressure the companies face to monitor and control content.

The new European Union "code of conduct on illegal online hate speech" states that Facebook, Google's YouTube, Twitter and Microsoft will review reports of hate speech in less than 24 hours and remove or disable access to the content if necessary.

European governments were acting in response to a surge in anti-Semitic, anti-immigrant and pro-Islamic State commentary on social media.