(Reuters) -Australian real estate firm REA Group ( RPGRF ) said on Monday it is considering acquiring London-listed peer Rightmove ( RTMVF ) via a possible cash and share offer.

REA Group ( RPGRF ), majority-owned by News Corp, said it had not yet approached or had any discussions with Rightmove ( RTMVF ) on a potential offer.

Rightmove ( RTMVF ), Britain's largest property portal, had a market value of 4.36 billion pounds ($5.73 billion), as of Friday's close.

Shares of Melbourne-headquartered REA Group, in which the Murdoch family owns more than 61%, fell as much as 5.9% to A$206.01 by 0053 GMT.

Rightmove ( RTMVF ) did not immediately respond to a Reuters' request for comment.

"There can be no certainty that an offer will be made," the Australian company said in a statement.

REA Group ( RPGRF ) now has to either lodge a firm bid for Rightmove ( RTMVF ) or back out by Sept. 30, according to the U.K.'s takeovers rule.

($1 = 0.7613 pounds)

(Reporting by Aaditya Govind Rao in Bengaluru; Editing by Subhranshu Sahu)