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MAINZ, Germany — A spate of Hundreds of sex assaults allegedly committed mostly by North African men on New Year's Eve in Cologne has sparked an "explosion in sales" of pepper spray and non-lethal guns, German officials and an industry chief said.

Authorities are investigating more than 670 criminal complains — almost 350 of them sexual offenses — after hundreds of women were groped and robbed by groups of men outside the main railway station in the western city.

"We saw a huge spike of sales numbers after January," said Ingo Meinhard, head of the German association for gunsmiths and weapons dealers.

The association expected purchases of "so-called deterrents and defensive small arms" to at least double in 2016 following the Cologne attacks, Meinhard told NBC News.

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“CS gas spray, stun guns and pepper spray are especially in great demand,” he added.

Related: Many Germans' Views on Foreigners Change After Sex Assaults

Two weeks after the mass incidents on New Year's Eve, the number of criminal complaints reached 676 on Friday — including 347 sexual offenses, Cologne prosecutor Ulrich Bremer said. Five suspects are in investigative custody.

In addition to defensive sprays, Cologne police said it had already received more than 300 applications from adults wanting to carry imitation handguns and so-called gas pistols.

This was compared to 408 licenses for these weapons issued during all of 2015, police spokeswoman Daniela Lindemann said.

Germany's strict gun laws mean that only hunters and professional marksmen are allowed to obtain licenses for lethal arms and would-be buyers are subject to background checks.

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Cologne prosecutors are now offering a reward of 10,000 euros ($11,000) for information leading to the arrest or identification of those who committed the sexual assaults and robberies on New Year’s Eve.

According to police, most of the suspects are North African men.

More than 1.1 million migrants and refugees arrived in Germany last year — including many who fled the civil war in Syria.