MILAN (Reuters) - Italian lender Monte dei Paschi di Siena (>> Banca Monte dei Paschi di Siena SpA) looks likely to increase a planned share sale to 5 billion euros (4.1 billion pounds), two billion euros more than first planned, to help it pass a Europe-wide bank health check and repay state aid.

An extraordinary board meeting was called for Friday after the bank said earlier this week it was evaluating how much capital it needs in light of the asset review to be conducted by the European Central Bank and after discussions with the Bank of Italy.

Two sources close to the matter told Reuters the bank was looking to increase the size of the cash call to 5 billion euros from 3 billion, and that it needed quick approval from the board in order to launch the revised share sale by June.

A third source, a banker familiar with the situation, said a bigger capital increase would allow Monte dei Paschi to increase the coverage of doubtful loans in view of the ECB exam as well as take advantage of the positive mood in the market to strengthen its balance sheet.

Italian banks are cleaning up their accounts by setting aside billions of euros to cover for losses on bad loans, which have been rising sharply during the longest recession since World War Two.

But while Intesa Sanpaolo (>> Intesa Sanpaolo SpA) and UniCredit (>> UniCredit SpA), the top two banks, booked a combined 21 billion euros in provisions for bad debts last year to raise their coverage levels to 46 percent and 52 percent respectively, Monte dei Paschi has lagged behind.

The Tuscan lender, the world's oldest, set aside 2.75 billion euros for bad debts in 2013, and its coverage ratio of impaired loans stands at a lowly 42 percent, a level which analysts say is likely to fall short of the ECB requirements.

Adding to the pressure, Monte dei Paschi has pledged to pay back this year 3 billion euros of 4.1 billion euros in state aid it received, with the rest due by 2017.

"The market is going well. It's easier to raise funds now," the banker said, adding that other lenders may have to follow in Monte dei Paschi's steps. "Increasing the size of the cash call now means you don't need to do another one later."

BENIGN MARKET

In a sign that other lenders in weaker euro zone countries are seeking to benefit from more benign market conditions, National Bank of Greece (>> National Bank of Greece) won approval on Wednesday to raise up to 2.5 billion euros through a share offering.

The lender had wanted to raise the money by selling non-core assets but changed tack after the Greek central bank pressed it to follow domestic rivals which have already raised 2.95 billion euros between them from the markets.

Monte dei Paschi, hit hard by the euro zone debt crisis and a scandal over loss-making derivatives deals, is one of eight Italian banks under ECB scrutiny tapping investors for funds so far this year.

Altogether, they have announced plans to raise a combined 8 billion euros, which will increase to 10 billion euros if Monte Paschi approves a bigger cash call on Friday.

The bank's former controlling shareholder, the Monte dei Paschi foundation, has gradually cut its stake to just 2.5 percent, shaking up the shareholder structure which now includes BlackRock (>> BlackRock, Inc.) and Latin American investors Fintech and BTG Pactual.

(Additional reporting by Stephen Jewkes writing by Silvia Aloisi; editing by Mark Trevelyan and Tom Pfeiffer)

By Maria Pia Quaglia and Gianluca Semeraro