Jan 24 (Reuters) -

State-backed Italian bank Monte dei Paschi di Siena

(MPS) has launched a surprise 13.3 billion euro ($13.9

billion) all-share buyout offer for Mediobanca, it

said on Friday.

Monte dei Paschi, which was for years the problem child of

Italian banking until a 2017 bailout, said it was offering 23 of

its own shares for every 10 Mediobanca shares tendered,

equivalent to a 5% premium versus Thursday's closing price.

($1 = 0.9568 euros)