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MILAN, Oct 25 (Reuters) - Italy's Fondazione Cariplo on Tuesday approved a small investment in Monte dei Paschi di Siena , a source close to the charitable institution said, as the Treasury turned to more banking foundations to support the lender's new share issue.

The Treasury, which owns 64% of Monte dei Paschi (MPS) following a 2017 bailout and also oversees banking foundations, had initially secured a 30 million euro contribution from local foundations in the Tuscan bank's home region.

As the 2.5 billion euro cash call nears its conclusion next Monday, the Treasury has also knocked at the doors of banking foundations in Italy's wealthy north, three sources close to the matter said.

Lombardy-based Cariplo, an influential foundation which is a leading shareholder in top bank Intesa Sanpaolo, on Tuesday committed 10 million euros towards MPS' share sale, the first source said.

The steering committees of Turin-based Fondazione CRT and Compagnia di San Paolo also met to discuss the MPS investment this week, and two sources close to the matter said both foundations expected to give a positive answer to the Treasury's request in the coming days.

The price of MPS' shares has slipped below the 2 euros set for the new stock.

The rights to buy the new shares closed down more than 87.5% on Tuesday, the last day on which they can change hands, at 0.025 euros each.

That compares with an initial price of 7.837 euros for the subscription rights reserved for shareholders in MPS, which can be exercised until Monday.

The cash call is covered for up to 1.6 billion euros by Italian taxpayers, while the rest needs to come from private investors due to European Union state aid rules.

A group of eight banks and fund Algebris have guaranteed 857 million euros of the issue against the payment of hefty fees.

Banking foundations are not-for-profit entities which emerged as key shareholders in Italian banks when the industry was privatised in the 1990s.

Some have seen their wealth take a hit from the demise of banks they owned, such as MPS, and have later been forced by law to diversify their investment portfolios.

With fewer than 10 foundations participating in the cash call and contributions amounting at most to 10 million euros for each of them, the overall investment will remain below 100 million euros, a person with knowledge of the matter said. ($1 = 1.0029 euros) (Editing by Agnieszka Flak and Keith Weir)