BERGAMO, Italy (Reuters) - UBI (>> UBI Banca Scpa), Italy's fifth-biggest bank, does not rule out a tie-up with troubled Monte dei Paschi di Siena (>> Banca Monte dei Paschi di Siena SpA) but will not be pushed into an unwanted deal, its chief executive said on Saturday.

UBI is one of 10 cooperative banks that the government is forcing to convert into joint-stock companies within 18 months.

The reform, which scraps voting rules that had been seen as an obstacle to bank mergers and acquisitions (M&A), is expected to spur a wave of deals, and UBI is expected to play a prominent role.

The bank has been tipped as the most likely domestic bidder for Monte dei Paschi, which is not a cooperative bank but has been told by the European Central Bank to find a buyer quickly because of its stretched finances.

UBI Chief Executive Victor Massiah told reporters at a news conference on the sidelines of its annual shareholder meeting that the bank would not be forced by authorities and regulators into any tie-up that it does not like. Creating value for its own shareholders is the priority, he said.

Asked if that meant UBI was ruling out a deal with Monte dei Paschi, he said, "I cannot rule anything out, because transactions can be done in many different ways."

Another potential partner for UBI is Banco Popolare (>> Banco Popolare Societa Cooperativa), bankers say.

Massiah put the chances of a tie-up for his bank at 50 percent.

He said all M&A options were "open and possible" but that tie-ups were not inevitable, because fewer than half of mergers in the past have proved successful.

For the cooperative banks, he said, "The (M&A) synergies that are being talked about are in the hundreds of millions of euros, but the capital that is necessary is in the billions of euros. It has to be a very carefully considered move."

Foreign banks are not queuing up to buy lenders in the euro zone's third-biggest economy, he said, adding that UBI had not yet hired an M&A adviser and that there were no concrete proposals on the table.

"We can stay alone," Franco Polotti, the chairman of the bank's management board, said. "If there are opportunities to seize, we can do that, but we are not obliged to do it."

The bank said it expected to convert into a joint-stock company before its board is renewed in April 2016, probably this year.

(editing by Jane Baird)

By Silvia Aloisi and Andrea Mandala