Rupert Murdoch's News International has asked nine people who claim their phones were hacked by the newspaper group to provide more evidence, after apologizing for the first time to eight others on Friday.

The British newspaper arm of media giant News Corp has written to the nine individuals, who have instigated legal action against the group, a spokesman said on Monday.

Many more are thought to have had their phones hacked by journalists digging for stories at News International's Sunday tabloid News of the World, Britain's best-selling newspaper.

An investigation into the affair began years ago but has recently escalated into a national scandal that forced Andy Coulson, a former editor of the paper, to resign from his position as Prime Minister David Cameron's director of communications.

Until last Friday, News International had said any hacking that occurred was the work of rogue reporters. The tabloid's royal reporter and a private detective were arrested and jailed in 2005/06 for snooping on voicemail messages of royal aides.

The nine who have been asked for more evidence are actors Leslie Ash and Steve Coogan, ex-football executives David Davies and Mick McGuire, jockey Kieren Fallon, model Elle Macpherson's ex-legal adviser Mary Ellen Field, footballer Paul Gascoigne, ex-member of parliament George Galloway, and actor Jude Law's personal assistant Ben Jackson.

We interpret this as wanting to settle some claims at a very early stage, said Charlotte Harris of law firm Mishcon de Reya, which represents five of the 24 individuals with active court cases against the News of the World.

(Reporting by Georgina Prodhan and Olesya Dmitracova; Editing by Will Waterman)