South African construction group Murray & Roberts, currently the subject of a takeover bid by German investor ATON, said on Wednesday that an independent report showed that a fair offer for the company would be as much as 22 rand ($1.85) per share.

M&R renewed its call to shareholders to take no action regarding the proposed offer by ATON, which is expected to open on Friday, saying that the offer of 15 rand per share "materially undervalues Murray & Roberts based on its prospects and is opportunistic".

M&R, which last month rejected ATON's buyout offer which values the engineering and construction company at nearly $600 million, said on Wednesday that 20 to 22 rand per share was fair value based on a report that assessed the offer.

ATON, which already owns a third of M&R, made a buyout offer of 15 rand ($1.26) per share last month and believes the offer is still "significant and attractive".

"This view is demonstrated by two top ten shareholders having sold or agreed to sell a total of c. 9.6 percent of the issued share capital of M&R to ATON at 15 rand per share," ATON said in an emailed statement.

Last week, ATON bought 13,671,480 ordinary shares in the construction firm and also agreed to buy a further 29,005,926 shares from investment management company Allan Gray, M&R's third largest stakeholder, bringing its stake to 39.6 percent.

ATON, with a diverse portfolio of investments in the mining, engineering, aviation and health technology sectors, is making its second attempt at a deal after a previous approach failed in 2016. ($1 = 11.8922 rand)

- Reuters