Tech giants Facebook, Twitter, Microsoft and YouTube have joined forces and committed to efficiently combat hateful online content and terrorist propaganda as part of a new "code of conduct'' formulated and announced Tuesday by the European Union (EU).

The EU rules require the world's biggest social media firms to review the majority of hateful online content and to remove them within 24 hours when necessary. The rules also require them to identify and promote "independent counter narratives'' to hate speech and propaganda published online, reports the Christian News.

The move of the European Commission was prompted by the growing concern that terror organisations like the Islamic State (ISIS) have been utilising the sites to relay messages and instigate hatred against certain individuals or groups.

Vera Jourova, the EU commissioner responsible for justice, consumers and gender equality, said the code of conduct, which will be regularly reviewed in terms of its scope and its impact, "will ensure that public incitement to violence and to hatred has no place online."

"The Internet is a place for free speech, not hate speech," she said.

Under the agreement, the firms committed with the EU's executive arm to come up with internal procedures and staff training to guarantee that illegal contents are assessed and, where necessary, removed within 24 hours.

They have also agreed to strengthen their partnerships with civil society organisations who often flag content that promotes incitement to violence and hateful conduct. The European Commission and the firms have likewise agreed to support civil society organisations to deliver "anti-hate campaigns.''

For its part, Twitter assured to tackle the issue "head-on'' along with partners in industry and civil society. The site has been at the centre of much of the hate speech that's spread online over the past few years, reports say.

"We remain committed to letting the Tweets flow," said Twitter's European head of public policy Karen White. "However, there is a clear distinction between freedom of expression and conduct that incites violence and hate."

Monika Bickert, Facebook's head of global policy management, encouraged the company's 1.6 million users to use the site's built-in reporting tools should they find content they consider unacceptable.

"Our teams around the world review these reports around the clock and take swift action," she said.