(Adds Spinecap comment)
By Francesca Landini and Stephen Jewkes
ROME, Feb 1 (Reuters) - A consortium led by Italian state lender Cassa Depositi e Prestiti (CDP) has asked infrastructure group Atlantia ATL.MI to give it more time to submit "an improved and more compelling" binding bid for a stake in its motorway unit.
In a statement on Monday, Atlantia said the consortium, which also includes investment funds Blackstone (NYSE:BX) BX.N and Macquarie MQG.AX , had written a letter asking for time, until the end of February.
The binding offer was initially expected by the end of January, but a lengthy due diligence on Autostrade and Italy's ongoing political crisis have slowed down talks. negotiations are part of renewed efforts to end a long-standing dispute between Atlantia and the Italian government triggered by the 2018 deadly collapse of a bridge run by Autostrade.
Atlantia said the letter contained no details on price but said that compared to a previous valuation in December "we are confident of reaching a more considered outcome ... and to be able to provide an improved and more compelling proposal for your consideration".
Shares in Atlantia rose sharply on Monday, closing up 8.8%, reacting to a report by Bloomberg News saying the CDP-led consortium would value the entire Autostrade business at between 8.5 billion euros ($10.26 billion) and 9.5 billion euros, excluding debt.
Sources contacted by Reuters did not confirm that price range, with one source saying it was too early to discuss details of the offer.
Atlantia minority shareholder Spinecap said it believed the equity of Autostrade was worth at least 12 billion euros.
"Any deal lower than 10 billion euros for the 88% stake owned by Atlantia must therefore categorically be rebuffed," Spinecap founder Nicolas Ducarre said in emailed comments.
An equity value of 8.5-9.5 billion euros for Autostrade would be in line with the preliminary price range the consortium led by CDP had indicated in October last year.
In its statement, Atlantia said the offer made by the consortium in December, besides being below the group's expectations, had been lower than one made by the same consortium in October.
Atlantia, which is controlled by the Benetton family, is due to hold a board meeting on Feb. 5 when it will discuss the consortium's request for more time for its bid. ($1 = 0.8282 euros)