A US-based press organisation says it has documented 31 arrests of journalists in the United States this year.

The Committee to Protect Journalists (CPJ) says 10 of them were arrested while covering protests in St Louis.

These protests were reaction to the acquittal of a white police officer charged in the fatal shooting of a black man.

The arrests include the detention of the same people more than once.

The CPJ says press equipment was seized, stolen, or damaged at least 20 times - four cases of which took place during the presidential inauguration.

It has also documented 31 physical attacks on journalists - 22 of them were assaulted while covering protests.

It also says there were five incidences where journalists were stopped at the US border.

The group explains how it tracks border stops: "Journalists stopped at the border and subjected to prolonged, invasive questioning or who have their electronic devices searched or are asked to provide passwords.

"We count border stops even if we are unable to draw a direct connection between the stop and the journalist’s work activities, because the resistance of US authorities to provide information makes it extremely difficult to identify the motive".

The organisation says: "CPJ believes that when a country's journalists are silenced, its people are silenced.

"If journalism is under threat, so is your right to be informed and your ability to hold your government accountable.

"So this year, CPJ and the Freedom of the Press Foundation partnered with more than two dozen groups to launch the US Press Freedom Tracker, a website that documents threats to press freedom in the United States".

CPJ says the tracker is the first centralised source of data of its kind.