MILAN (Reuters) - Four Italian banks that were rescued from bankruptcy in November and are now in the process of being sold said on Thursday their non-performing loans had increased by 386 million euros ($432 million) in the first half of the year.

Italy is struggling to sell Banca Marche, Banca Etruria, CariChieti and CariFerrara in an effort to recoup at least part of the 3.75 billion euros that other Italian lenders stumped up in the rescue.

Sources familiar with the matter have said bids for the lenders were low as investors feared the banks would need to write down further their problem loans.

The four banks said they held 'sofferenze' -- or loans to insolvent borrowers -- worth 542 million euros in gross terms at the end of June.

This was up from 156 million euros six months earlier as loans previously considered as 'unlikely to pay' had now been classed as non-performing, they said. ($1 = 0.8928 euros)

(Reporting by Valentina Za)