Media playback is unsupported on your device Media caption Far-right protesters want the antifa declared a domestic terror organisation

Police arrested 13 people as far-right groups rallying in the north-western US city of Portland, Oregon, skirmished with left-wing counter-protesters.

A huge police operation kept the right-wing rally separated from supporters of the antifa, or anti-fascist movement.

Small clashes that did take place occurred as the rival factions moved away after the rally.

Rally organisers were calling for antifa to be declared a domestic terror organisation.

Portland, one of the most liberal cities in the US, is regarded as an antifa stronghold.

How did events unfold?

Police said they seized weapons including metal poles and shields from both sets of protesters.

At least six people suffered minor injuries and one person was taken to hospital.

Image copyright AFP Image caption Protesters confronted right-wing groups at a waterfront park in Portland

Portland Police Chief Danielle Outlaw said those arrested faced charges including disorderly conduct, interfering with police, resisting arrest and unlawful use of a weapon.

At the height of the demonstrations there were about 1,200 people on the streets of the city centre, she told a news conference.

Who attended the rally?

The rally had mainly been promoted by Joe Biggs, a member of the far-right Proud Boys group and former employee of Alex Jones's Infowars.

Proud Boys - which The Southern Poverty Law Center, a major US civil rights organisation, has classified as a hate group - have been involved in previous far-right rallies, and violent street clashes, in Portland.

Proud Boys says incidents of violence allegedly involving members of the loosely organised antifa movement, an international coalition of militant activists and protesters opposed to the far right - justifies a ban.

Members of the local Rose City Antifa group mounted the counter-demonstration in the city.

A statement on its website accused far-right groups of planning "to bring their branded political violence to our streets" and encouraged people "to defend Portland against far-right attack".

As well as Proud Boys, a number of other far-right groups said they would be there - including the American Guard, which the Anti-Defamation League has called "hardcore white supremacist", and the militia group Three Percenters.

What's the background?

It follows two years of increasingly violent rallies in Portland, many of which were organised by Joey Gibson, the leader of far-right group Patriot Prayer, who is currently facing criminal charges connected to a right-wing riot outside a bar in May.

But organisers said this particular rally was a response to an incident said to have taken place at the last far-right rally held in the city, in June.

President Donald Trump had said the Portland situation was being closely watched by his administration, and indicated that naming antifa "an organisation of terror" was being considered.

Skip Twitter post by @realDonaldTrump Major consideration is being given to naming ANTIFA an “ORGANIZATION OF TERROR.” Portland is being watched very closely. Hopefully the Mayor will be able to properly do his job! — Donald J. Trump (@realDonaldTrump) August 17, 2019 Report

Mr Trump has previously mentioned white supremacists, as well as antifa as being a major issue.