By Andrea Mandala and Gursimran Mehar

MILAN (Reuters) -Italy's fourth-largest bank BPER on Thursday joined in a raft of takeover bids rocking the country's financial sector, with a 4.3 billion euro ($4.46 billion) all-share bid for Banca Popolare di Sondrio.

BPER and Popolare di Sondrio (BPSO) have in common their main shareholder, insurer Unipol, which distributes its products through both banks.

BPER said it would issue 29 new shares for every 20 shares of BPSO shares tendered, implying a premium of 7.8% based on Thursday's closing prices, according to Reuters calculations.

BPER said the premium is of 6.6% based on Wednesday's closing levels, but both BPER and BPSO shares gained over 4% on Thursday.

BPER said it aimed to secure at least 35% of BPSO's capital plus one share in order to exert control over the rival.

The combined company's net profit is expected to surpass 2 billion euros in 2027, BPER said adding that it expects the deal to close in the second half of 2025.

BPER's market capitalisation of about 9.74 billion euros is more than double mid-sized lender BPSO's market value of 4.17 billion euros, according to LSEG data.

Though Unipol boss Carlo Cimbri had previously said that a merger between BPER and BPSO would be "a mistake," the combination had been widely expected to take place at some point in the future.

The bid comes as a number of unsolicited buyout offers are set to redesign Italy's banking landscape.

Before Christmas, BPER's direct rival Banco BPM launched a bid for asset manager Anima Holding and took a stake in bailed-out Monte dei Paschi di Siena, before becoming a takeover target for UniCredit.

Then earlier this year, state-backed Monte dei Paschi launched a hostile 13.3 billion euro all-share bid for prestigious rival Mediobanca.

Unsolicited offers are traditionally rare in the finance industry. But Intesa Sanpaolo led the way back in 2020 by acquiring smaller rival UBI after a strenuous takeover battle.

BPER reported full-year adjusted consolidated net profit of at 1.40 billion euros, the Modena-based bank said in a separate statement.

($1 = 0.9634 euros)

(Reporting by Andrea Mandala in Milan and Gursimran Kaur in Bengaluru; Editing by Shounak Dasgupta and Valentina Za)