MANILA, Philippines - Monday afternoon’s reported killing of at least 13 journalists in Maguindanao was a “dark day for press freedom,” an international watchdog said Tuesday.

In a statement on its website, the Reporters Without Borders said it could be the largest casualty of journalists in any one incident.

“Never in the history of journalism have the news media suffered such a heavy loss of life in one day,” Reporters Without Borders said. “We convey our condolences and sympathy to all journalists in the Philippines, who are in state of shock after this appalling massacre.”

The press freedom organization added: “We have often condemned the culture of impunity and violence in the Philippines, especially Mindanao. This time, the frenzied violence of thugs working for corrupt politicians has resulted in an incomprehensible bloodbath. We call for a strong reaction from the local and national authorities.”

Nonoy Espina, vice chairman of the National Union for Journalists of the Philippines (NUJP), agreed with the assessment. “The incident is more chilling because we are not a war area. This is a deliberate killing. These journalists were not just caught in a crossfire.”

He added that the abduction and execution of journalists and civilians in Maguindanao was evidence of a breakdown of law and order and a loss of governance.

Espina, who came from a recent trip to the area, said it was impossible authorities in the area did not know violence would soon erupt.

“There is no government in Maguindanao. It is not only a total breakdown of law and order but a total loss of governance,” Espina said.

He also called on government to get to the bottom of the incident.

“This would be a litmus test for government. If they don’t crack down, we might as well wave government goodbye,” Espina stressed.