The website and Twitter feed of the Financial Times (FT) have been hacked, apparently by the "Syrian Electronic Army", a group of online activists who say they support Syrian President Bashar al-Assad.
The group on Friday 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 Jabhat al-Nusra Syrian rebel group executing blindfolded and kneeling members of the Syrian army.
The video could not be independently verified.
"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 newspaper's press office said.
Twitter was not immediately available for comment.
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.
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 FT is the latest media organisation under attack by the group, which was also behind last month's incident involving the AP news agency.
In that hack, the Syrian Electronic Army took control of AP's official Twitter feed and sent out a bogus message that two explosions at the While House had injured President Barack Obama.
The false tweet triggered the US financial markets to take a brief but steep plunge.
"Twitter has become a big enough media outlet that they should provide better security for high-value accounts like the Associated Press, the FT and others," said Mikko Hypponen, chief research officer with security software maker F-Secure.
The Syrian Electronic Army has claimed credit for hacking various news organisations including Al Jazeera and Agence France-Presse.