By Carlos Ruano and Paola Arosio
MADRID/MILAN (Reuters) - Italy's Atlantia (MI:ATL) on Thursday opened the door to considering a full cash offer for Spain's Abertis (MC:ABE), but said for now it still wanted some investors to accept shares in its 16.3 billion-euro bid to buy the Spanish toll road firm.
Atlantia made a cash-and-share offer for the Spanish firm in mid-May in an attempt to create the world's biggest toll road company and said it wanted at least 10 percent of Abertis shareholders to accept payment in shares.
In a prospectus filed with Spain's stock market regulator on Thursday, Atlantia said it was still insisting on some shareholders accepting payment in shares.
However, it suggested it could consider a full cash offer, although it said such a move would require asking Spanish regulator CNMV "for permission to modify the terms of the offer ... extending the cash offer to the entirety of Abertis shares."
Atlantia would not comment on whether it would go ahead with asking for a change in terms.
The Italian infrastructure company, which is controlled by the Benetton family, wants to win support from Abertis shareholders representing at least 50 percent plus one share.
This has shone a spotlight on Criteria Caixa, the holding company that controls Spanish lender Caixabank and which is the biggest shareholder in Abertis with a 22.3 percent stake.
A source close to the matter said changing terms of the bid to make it an all-cash offer could sweeten Atlantia's proposal and lure smaller investors in Abertis.
"A move to change the offer to an all-cash deal would make Criteria Caixa less relevant for the outcome of the deal," the source told Reuters.
Industry analysts have said Criteria Caixa could be interested in swapping its shares in the Spanish firm with Atlantia's, while other investors could be more interested in cash.
Abertis said on Thursday it did not expect to respond to Atlantia's offer until it had been approved by the regulator, a process that usually takes two or three months.
Criteria Caixa said it would not comment until Abertis responded.
Atlantia maintained its offer of 16.5 euros per Abertis share on Thursday and confirmed its approach was a friendly one. The Spanish company's stock closed at 16.42 euros.
Atlantia intended to "meet strategic interests of Spain" in relation to stake held by Abertis in satellite operator Hispasat, the Italian company said.
The Spanish government can block the transaction.
(Additiona reporting by Francesca Landini, writing by Sarah White; and Francesca Landini; Editing by Julien Toyer and Edmund Blair)