North Rhine-Westphalia interior minister Ralf Jaeger is under pressure to resign, after it was reported that officials demanded the word 'rape' be removed from a police report on the New Year's Eve sex attacks in Cologne.

More than 130 cases of rape and sexual assault were reported during the city's New Year's Eve celebrations, with groups of refugee and immigrant men alleged to be responsible.

"KHK [the police officer involved] told me that the state control centre wanted the report cancelled and the expression 'rape' deleted," officer Joachim H wrote in an internal memo obtained by Expressen newspaper.

The two officers were on duty in Cologne police station when the initial report on the attacks was being written. The report was entitled "rape, sexual harassment, thefts, committed by a large group of foreign people".

Senior officer KHK allegedly received a phone call requesting the removal of the word 'rape' at the "the wish of the state interior ministry", with the dispute concerning the description of an attack on a 19-year-old woman. Police refused to alter the report.

News of the attacks broke days later in the media, sparking widespread criticism of chancellor Angela Merkel's open door refugee policy. Subsequent accusations of a police cover up forced the resignation of the city's police chief.

The latest revelations have heaped pressure on state interior minister Ralf Jaeger, with opposition parties in the state parliament calling on the Social Democrat to resign. In a statement, Jaeger's office denied the allegations of a cover up, but said that a discussion on the "criminal classification" of the attacks took place between the state police control room and Cologne police.