London - British Prime Minister David Cameron on Tuesday condemned Facebook as "irresponsible" after the social networking site lifted its ban on users posting videos of beheadings.Cameron said "worried parents" needed to hear an explanation from the US-based website."It's irresponsible of Facebook to post beheading videos, especially without a warning," the prime minister said on his Twitter page."They must explain their actions to worried parents."Facebook had introduced a temporary ban on videos of beheadings in May following complaints that the graphic footage could cause users long-term psychological harm.But it confirmed on Monday that it had reversed the decision on the grounds that the site is used to share information about world events, including terrorist attacks and human rights abuses.It added, however, that it was considering adding warnings to graphic videos and that photos or videos that "glorify violence" would be removed."Facebook has long been a place where people turn to share their experiences, particularly when they're connected to controversial events on the ground, such as human rights abuses, acts of terrorism and other violent events," the company said in a statement."People are sharing this video on Facebook to condemn it. If the video were being celebrated, or the actions in it encouraged, our approach would be different."However, since some people object to graphic video of this nature, we are working to give people additional control over the content they see."This may include warning them in advance that the image they are about to see contains graphic content."More than one billion people around the globe use Facebook every month, according to the website, which was founded in 2004 by Mark Zuckerberg and four fellow students at Harvard University.