Hollywood star George Clooney on Friday rejected an apology from Britain's Daily Mail over a story claiming his fiancee's mother opposes the couple's upcoming marriage, accusing the tabloid of cover-up.

The paper reported earlier this week that the US actor's soon-to-be Lebanese mother-in-law had been telling "half of Beirut" that she opposes the union between the heartthrob and her daughter Amal Alamuddin due to her supposed Druze faith.

The daily removed the piece from its widely read website and apologized following an initial protest by Clooney, 53, who said it got many key facts wrong.

The publication however maintained that its story was "not a fabrication, but supplied in good faith" by a reputable journalist.

A clearly incensed Clooney is not letting the matter go, issuing a second USA Today opinion piece Friday in three days.

"There is one constant when a person or company is caught doing something wrong. The cover up is always worse," Clooney wrote.

"In the apology, managing editor Charles Garside claims that the article was 'not a fabrication,' but 'based the story on conversations with senior members of the Lebanese community,'" he added.

"The problem is that none of that is true... So either they were lying originally, or they're lying now."

Word that Alamuddin, 36, a Lebanon-born London lawyer, had stolen the heart of one of Hollywood's most celebrated bachelors caused an international media frenzy back in April.

No official details have been released on when the high-profile pair will say "I do."