Police are on high alert ahead of Germany’s traditional carnival celebrations this week after social media connected to the Islamic State militant group called for attacks targeting revellers in Cologne and Nuremberg, said police spokespeople.

Bild newspaper reported that a German-language propaganda site run by IS had published a computer-created collage image calling on viewers to “choose your next attack target” and listed the dates and locations of upcoming carnival events.

The Festival of Love planned in the Dutch city of Rotterdam in early March was also listed as a target on the collage featuring a bloody knife and the hashtag #LetsSlaughter.

Germany experienced a series of high-profile attacks, including a car-ramming and stabbings, with Islamist connections in the lead-up to national elections on February 23.

The week-long carnival celebrations, which kick off on Thursday, take place in some predominantly Catholic southern and western parts of Germany, with revellers packing the streets to party, consume large quantities of alcohol and dance.

It is particularly popular in Rhineland cities such as Cologne and Duesseldorf, where festivities peak on "Rose Monday" next week with tens of thousands attending street parades featuring comical or satirical floats.

Cologne police said operational planning for the events was being adapted to take the threat into account, but they said the collage could be scaremongering aimed at unsettling the population rather than evidence of an imminent threat.

More than 1,400 officers will be stationed at known hotspots, emergency services will be out in full force and there will be bag and personal searches of carnival goers.

Carnival organisers in the Bavarian city of Nuremberg, said on Wednesday that an event targeted on the IS-related website, the International Carnival Parade, had been cancelled due to concerns expressed by the venue.

About 50 people had been expected at the event at the Saigon Bar in central Nuremberg, said organiser Global Locals.

Nuremberg police said they were aware of the Islamic State threats, which were being evaluated by state security services.

They said there was no indication of a concrete plot for an imminent attack.