BERLIN • Cologne is on high alert ahead of its giant carnival festivities since a shocking spate of sexual assaults, with the German authorities anxious to prevent a repeat of the rampage and ward off potential militant attacks.

Police in the western German city have been struggling to restore public confidence after it emerged that hundreds of women were groped and robbed in a mob of mostly North African and Arab men during New Year celebrations.

Around 1,000 complaints have been filed over the crime spree that has also ignited an intense debate about Germany's ability to integrate 1.1 million asylum seekers it took in last year.

The carnival festivities kick off on Thursday with street parties - a week-long binge of beer, song and dance by revellers in fancy dress - and run through Ash Wednesday on Feb 10.

Some 2,500 police officers have been called in to patrol the streets, three times as many as last year, as the security budget reached €360,000 (S$556,000).

Closed-circuit television cameras have been installed and bans imposed on known petty thieves.

A "security point" for women will be set up in the city, to be staffed by social workers and psychologists, and the local judicial system geared up to accelerate the processing of any potential offenders during the festivities.

As doubts surfaced over the cultural differences of the mostly Muslim newcomers, the carnival's organisers have printed a leaflet in both Arabic and English explaining the party to newcomers, including whether alcohol was a must.

"While many Cologne locals drink beer or other alcoholic beverages during carnival, it is of course not compulsory. You can have fun, sing and dance just as easily without alcohol," according to the flyer.

The neighbouring city of Bonn was more explicit in its advice to refugees, explaining that the word "buetzen" means "kissing somebody on the cheek, one of our carnival customs", but adding that "sexual overtures are strictly prohibited. Women and men must always consent to the 'buetzen'. No means no!"

But a repeat of the New Year debacle was not the only threat.

Security forces are also working to prevent a possible terror attack, with Germany's domestic intelligence chief Hans-Georg Maassen reiterating in a report that the situation remained serious after the Paris militant attacks in November.

The wider area around Cologne in North Rhine-Westphalia state is home to Germany's biggest concentration of radical Islamists.

Despite the fears, Chancellor Angela Merkel urged revellers not to shy away. "Because we're going to show that we won't let anyone keep us from enjoying life or having fun," she said. "We love our freedom, our freedom of expression and especially our freedom to have fun."