The website and Twitter feed of British newspaper the Financial Times were hacked on Friday, apparently by the "Syrian Electronic Army", a group of online activists who say they support Syrian President Bashar al-Assad.
The group posted links on the newspaper's Twitter feed to a YouTube video, uploaded on Wednesday, which purports to show members of the al Qaeda-linked Nusra Front Syrian rebel group executing blindfolded and kneeling members of the Syrian army.
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The video could not be independently verified.
Hacking attacks on verified Twitter accounts of media organisations have triggered urgent calls for the micro-blogging website to increase account security, particularly for news outlets.
"Various FT blogs and social media accounts have been compromised by hackers and we are working to resolve the issue as quickly as possible," a statement from the FT press office said. The paper is owned by Pearson Plc
Twitter was not immediately available for comment.
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Stories on the FT's website had their headlines replaced by "Hacked By Syrian Electronic Army" and messages on its Twitter feed read: "Do you want to know the reality of the Syrian 'Rebels?"', followed by a link to the video.
The group has previously targeted the Twitter account of the BBC's weather service, and those of Human Rights Watch and French news service France 24.
In the most disruptive incident so far, someone took control of the Twitter feed of U.S. news agency the Associated Press last month and sent a false tweet about explosions at the White House that caused financial markets to plunge.