Poland's broadcasting regulator moved Wednesday to justify its 350,000 euro ($410,000) fine for the American-owned television station TVN24, after the decision drew criticism from the US State Department and a media watchdog.

The National Broadcasting Council (KRRiT) accused the station, one of the country's two leading private news channels, of giving "a one-sided presentation of events" in coverage of protests against the government last year.

KRRiT spokeswoman Teresa Brykczynska had said the broadcaster "failed to inform viewers that the December 16-18 protests held outside parliament were unlawful, and for urging viewers to participate in the illegal protests."

During the December 2016 protests against the rightwing government led by the Law and Justice party (PiS), dozens of opposition lawmakers occupied parliament's main chamber over plans to ban journalists from parliament, a measure it later dropped.

PiS leaders accused the opposition of trying to stage a coup d'etat as thousands of demonstrators rallied outside parliament.

TVN24, which belongs to Discovery Communications, rejected the allegations and said it would appeal the fine that it received on Monday.

The channel says its coverage of the protests was balanced, noting that it had run live broadcasts and rebroadcasts of speeches made by PiS leader Jaroslaw Kaczynski.

Media watchdog Reporters Without Borders had said Tuesday that it was "alarmed by the record fine," which it sees "as designed to throttle a media outlet that is critical of the government."

The US State Department expressed "concern", saying "this decision appears to undermine media freedom in Poland, a close ally and fellow democracy."

In response to the State Department's statement, the KRRiT said that "bias was not the reason for the fine," adding that "TVN has the right to sympathise with the opposition. Yet the journalists' commentary could have fuelled aggression that could have led to tragic consequences."

In its statement Wednesday, the regulator singled out an on-air quote by Piotr Stasinski, deputy editor in chief of the liberal Gazeta Wyborcza daily, who was a TVN24 guest during the broadcasts in question.

At one point Stasinski said "lawmakers should block the (parliament) chambers as long as possible".

KRRiT said the broadcaster "had influence over the circle of guests invited to the studio" and "could and should have reacted when the opinions expressed were excessive, not based on facts or could constitute for an average viewer an incitement to activities against the law."

Since taking office in October 2015, the PiS government has been accused by media and rights groups of seeking to limit press freedoms, including by increasing state control over public broadcasters.

In July, the European Union called for an end to the "intimidation" of journalists critical of the PiS government, saying that media freedom should be respected.