Facebook pledged Monday to combat racist hate speech on its German-language network amid an upsurge in xenophobic comments online as Germany faces an unprecedented influx of refugees.

The US social media network said it would encourage "counter speech" and step up monitoring of anti-foreigner commentary, as company representatives were due to meet German Justice Minister Heiko Maas later Monday.

Facebook said it would work with other organisations in Germany "to develop appropriate solutions to counter xenophobia and racism and to represent this online".

It also urged users to report offensive postings and announced a partnership with the group Voluntary Self-Monitoring of Multimedia Service Providers (FSM).

As Germany faces a record influx of refugees and a backlash from the far right, social media such as Facebook have seen an upsurge of hateful, xenophobic commentary.

Opposition Greens party co-chief Katrin Goering-Eckardt several days ago read out in a YouTube clip a litany of verbal attacks that had been posted on her Facebook page, and urged the company to "finally ensure that such hatred and filth" is deleted.

She said freedom of expression is important but "has its limits when it comes to agitation to commit violence, or sickening hate speech".

Many users say that when they complain to Facebook about offensive posts, the network often responds that after a review the post does not violate its community standards.

Users also accuse the company of double standards for cracking down swifter and harder on nudity and sexual content than on hate-mongering.

Maas said Facebook was required to delete posts in violation of German laws against incitement of racial hatred.

In his invitation to company executives he said he wanted to talk about "improving the effectiveness and transparency of your community standards".

Facebook said it was "convinced that social media can be used effectively to discuss and question views such as xenophobia".

The vast majority of Germany's 27 million Facebook users did so in a very positive way, said Eva-Maria Kirschsieper of Facebook Germany.

"We are seeing that many groups are organising humanitarian aid for new refugees on our platform," she said.

Maas has for weeks urged Facebook to delete racist comments and threats that have targeted politicians, artists and volunteers helping refugees.

Weeks ago Germany's most popular film star, Til Schweiger, blasted fans who left dozens of anti-immigrant comments on his Facebook page after he appealed for donations for a refugee charity.

And a German TV journalist's impassioned appeal last month for an "uprising of decent people" against racism and attacks on asylum-seekers was viewed more than five million times via Facebook alone within 48 hours, drawing an outpouring of both support and scorn.

Facebook said in April it would not allow the social network to be used to promote hate speech or terrorism as it unveiled a wide-ranging update of its global community standards.