German police have detained two teenage boys and two teenage girls on suspicion of planning an Islamic State-style knife and firebomb attack on churches.

Three of the four suspects, all teenagers aged 15-16, were arrested in the state of North Rhine-Westphalia and are “strongly suspected of planning an Islamist-motivated terror attack and of having committed to carrying it out” according to prosecutors in Dusseldorf.

The fourth suspect, 16, was arrested in Stuttgart on “suspicion that he was preparing a serious crime endangering the state”, prosecutors there said.

Bild, a German tabloid, said the group had been planning to attack Christians in churches as well as police officers, adding that they were supporters of Islamic State (IS).

They are alleged to have discussed an attack that would have involved knives, Molotov cocktails and potentially guns. The assault was in an early stage of planning according to German media reports, which suggested that the potential targets were in Dusseldorf, Dortmund and Cologne.

It was not immediately clear if the alleged plot had any links with Isis-K, a dangerous offshoot of IS which was behind a massive terrorist attack on a concert hall in Moscow in March.

It comes after German police in January arrested three people who were planning an attack on Cologne cathedral on New Year’s Eve. Bild reported that those suspects were Tajik citizens acting for Isis-K.

Referring to the most recent arrests, a security source told Bild: “This case exemplifies the great danger of how quickly young people can be radicalised online and then plan attacks. Even those that were not previously on the radar of the security authorities.”

Germany has been on high alert for Islamist or other terrorist attacks since the outbreak of the Israel-Hamas war in Gaza on Oct 7.

It has previously suffered IS-inspired attacks, such as a deadly truck rampage through a Berlin Christmas market in December 2016 which killed 12 people.