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Facebook COO Sheryl Sandberg has expressed regret over her company's oversight in regards to its removal of an iconic Vietnam War photo.

The platform's deletion of the image from several accounts, only to later reinstate it, resulted in a damning report from Norwegian newspaper Aftenposten that criticized Facebook CEO Mark Zuckerberg for curtailing press freedom.

One of the users that published the Pulitzer prize-winning photo only to have Facebook remove it was Norway's Prime Minister Erna Solberg. The social network claimed the photo, which depicts a naked girl fleeing from a napalm attack, violated its nudity policy. In response, Solberg released a statement calling on Facebook to "review its editing policy." The PM added that Facebook was editing "our common history."

Sandberg has since penned a letter to Solberg addressing the incident, reports Reuters. "These are difficult decisions and we don't always get it right," wrote the Facebook COO. "Even with clear standards, screening millions of posts on a case-by-case basis every week is challenging."

Sandberg claimed in the letter that it was a sign of "how seriously we take this matter and how we are handling it," her remarks echoing Zuckerberg's reaction to the Trending topics controversy that mired the company earlier this year.

"Sometimes … the global and historical importance of a photo like 'Terror of War' outweighs the importance of keeping nudity off Facebook," wrote Sandberg.

In an interview with Norwegian broadcaster NRK, Solberg appreciated the response. "It shows that it helps to use your voice to say 'we want a change'. I'm very pleased with that," she said.

Facebook is currently treading a fine line when it comes to the policing of its unparalleled social network. On the one hand it is increasingly being pressured into removing sensitive content by governments and law enforcement agencies. This was evidenced in its recent bid to quell the critical rhetoric from Israeli lawmakers by agreeing to work with the country to tackle incitement on the social network.

However, like other social media sites, Facebook is also trying to distance itself from controversial content on its platform by arguing it cannot be held accountable as it does not publish the material itself. Just this week, Facebook tried (and failed) to block a teenage girl's lawsuit that claims it is liable for allowing a nude photo to repeatedly be shared on the site. Again, Facebook claimed that an EU directive provided it with protection from policing its entire platform over what is posted by an individual publisher.

Additionally, a committee of UK politicians recently demanded Facebook devote more staff members to the reporting and removal of sensitive content, in particular posts of an extremist nature. It all amounts to form a worrying trend for a company that is already pushing ahead with automating vast amounts of its platform.