MILAN - The board of Italian infrastructure group Atlantia said on Thursday it would launch a dual-track process to sell its 88% stake in motorway unit Autostrade per l'Italia, seeking to unblock negotiations with the government over the future of the business.

The government has been threatening to strip Autostrade of its concession since August 2018 when a motorway bridge operated by Autostrade collapsed in Genoa, killing 43 people.

The dispute appeared to have been resolved on July 14 when the government approved a plan that would see Atlantia pull out of the Autostrade business to make room for state lender CDP.

But that agreement risks unravelling because of disputes over its impact on minority shareholders in both Atlantia and Autostrade, and the sequencing of events to resolve the concession dispute. 

Atlantia said on Thursday it would press ahead with the sale of the stake in Autostrade through a competitive process or, as an alternative, a partial, proportional demerger of the stake with a view to listing the company on Milan's stock exchange.

"The dual-track process is open to both CDP and other Italian and international institutional investors," Atlantia said in a statement, adding it hoped to quickly overcome difficulties in talks with the state lender.

The infrastructure group controlled by the Benetton family also said that both the competitive auction and the demerger were subject to certain conditions, including the finalisation of an agreement with the transport ministry to settle the dispute over Autostrade's concession.

The government has insisted so far that it can only halt measures to revoke Autostrade's motorway contract once the ownership issue is settled and CDP gets control of the unit.

Atlantia has so far resisted, saying it wanted that threat removed before a deal was finalised.

A shareholder meeting is convened on Oct. 30 to vote on the demerger proposal.

(Reporting by Francesca Landini Editing by Keith Weir) ((francesca.landini@thomsonreuters.com; +39 02 66129437; Reuters Messaging: reutersitaly.thomsonreuters@reuters.net))