Tuscany's bailed-out Monte dei Paschi had unexpectedly launched a 13-billion-euro all-share takeover proposal for Mediobanca.

Italian bank Mediobanca on Tuesday rejected a takeover offer by state-backed rival Monte dei Paschi di Siena , saying a tie-up would be detrimental to its shareholders because it lacked any strategic and financial rationale.

Italian bank Monte dei Paschi di Siena has announced it is launching a 13.3 billion euro takeover bid for larger peer Mediobanca in a surprise move that could reshape the country’s banking sector.