ROME (Reuters) - Italy's shipbuilder Fincantieri is set to buy Leonardo's submarine business, known as Whitehead Alenia Sistemi Subacquei (WASS), with the deal expected to be announced later on Thursday, sources said.

Fincantieri will be financing the acquisition, worth 250-300 million euros ($268.20- $321.84 million) through a recapitalisation of up to 500 million euros, one of the sources told Reuters.

The difference between the value of the deal and the total recapitalisation will be used by the shipbuilder to further develop its defence business, a fast-growing sector on which the state-controlled company is betting, the source added.

Both Fincantieri and Leonardo are state-controlled and listed on the Milan stock exchange.

(Reporting by Giulia Segreti, editing by Alvise Armellini)