COLOGNE, GERMANY: Riot police broke up far-right protesters in Cologne on Saturday as they marched against Germany's open-door migration policy after asylum seekers were identified as suspects in assaults on women on New Year's Eve.

The attacks, ranging from sexual molestation to theft, shocked Germany, which took in 1.1 million migrants and refugees in 2015 under asylum laws championed by Chancellor Angela Merkel, despite fervent opposition.

Shortly before Saturday's protest began, Merkel hardened her stance toward migrants, promising expulsion for criminals and a reduction inmigrant numbers over the longer term to Germany.

Police said around 1,700 people attended the rally organised by the far-right anti-Islam PEGIDA movement, which has seized on the alleged involvement of migrants in the Cologne attacks as proof Merkel's policy is flawed.

Demonstrators, some of whom bore tattoos with far-right symbols such as a skull in a German soldier's helmet, had chanted "Merkel must go" and "this is the march of the national resistance". "Rapefugees not welcome," one banner read.

A police spokesman said roughly half of those at the PEGIDA movement were from the 'hooligan scene'. Some in the crowd threw bottles and fire crackers at officers, and riot police used water canon to disperse the protesters.

Two people were injured in the clash, and police detained a number of demonstrators, a Reuters witness said.

PEGIDA, or Patriotic Europeans Against the Islamisation of the West, almost fizzled out last year when its leader resigned after a photo was published of him posing as Adolf Hitler.

But its ranks have swelled as resentment spread of Merkel's welcoming stance to refugees.

In all, about 1,700 police officers were on the streets of Cologne, dwarfing the number on duty during the chaotic scenes of New Year's Eve when at least 120 women were robbed or sexually molested.

"The events on New Year's Eve led to a lot of emotion," said a police spokesman. "We had feared that emotions would boil over."

About 1,300 people attended a rival left-wing protest in Cologne, according to police.

"No means no. Keep away from our bodies," read one sign held by one of the demonstrators, most of them women.