A group of seven men sang a war-chant favoured by the Islamic State and tried to recruit fellow passengers while riding on the Berlin U-Bahn railway.

Berlin police are investigating after a large group of suspected radical Islamists rode the underground train while prostelysing for the Islamic State late on Thursday night. Eye witnesses said they sang an Islamic song, spoke in Arabic and handed out leaflets about the Islamic State.

Engaging other passengers in Arabic between stops in the historic centre of the city, one witness said the men were obviously “advertising” for the Islamic State, reports Focus.

Police are now reviewing security footage. A police spokesman said the force has determined the show was in support of a terrorist organisation.

The song was a so-called ‘Jihad Nashid’, a call to war sung in chant which is compatible with the strict orthodox Muslim rules forbidding music. In the Islamic State music is banned, but singing unaccompanied is allowed, a situation which over the course of Islamic history has given a rise to polyphonic chant not unlike some early European religious music.

There are a number of radical Islamists presently at liberty in Germany that the government is aware of. There are at least 670 Salafist Muslims in Berlin alone — a radical sect that wishes to impose conservative Islamic values on the world. The German government understands over half of these are violent individuals and many are allied to the Islamic State.

While many Islamists go free, the German government this week also took steps to curtail some freedom for religious fanatics. Police closed a radical mosque in Baden-Württemberg which had raised money for the Islamic State and had been a place of prayer for a fifth of all known German Jihadists who travelled to the Islamic State to fight.

The Islamic Educational and Cultural Center Mesdschid Sahabe had been visited by radical Salafist preachers and while property was seized by the state it is presently unclear whether any arrests have been made.