* Four suitors vying for UniCredit's Pioneer
* Amundi offered 4 bln euro in non-binding bid
* Poste Italiane looking for a partner to sweeten offer (Adds quotes and details)
By Francesca Landini and Gianluca Semeraro
MILAN, Oct 6 (Reuters) - France's Amundi has madea higher than expected 4 billion euro ($4.5 bln) offer to buyUniCredit's Pioneer Investments, two sources toldReuters, raising the bar in the race to snap up Italy'sthird-largest asset manager.
Three other suitors are vying for Pioneer - an Italianconsortium led by national post office Poste Italiane,Australia's Macquarie and British group Aberdeen AssetManagement, sources have said.
UniCredit's recently appointed CEO Jean Pierre Mustier islooking to sell Pioneer and other businesses - including onlinebroker Fineco Bank and Polish lender Pekao Bank - to boost the bank's stretched capital base.
Pioneer's value had previously been estimated at around 3billion euros.
Sources familiar with the matter told Reuters last week thatItaly's biggest lender by assets may need to raise as much as 16billion euros through asset disposals and a planned share sale.Netting 4 billion euros for Pioneer would help the bank reducethe size of the rights issue.
Amundi, Europe's biggest asset manager, and UniCreditdeclined to comment.
Shares in UniCredit rose nearly 3 percent on expectationsAmundi's offer, which was first reported by Il Messaggero dailyon Thursday, would force the other bidders to sweeten their ownoffers.
One source said Poste Italiane, which is leading aconsortium made up of state holding firm Cassa Depositi ePrestiti and domestic asset manager Anima Holding, wasnow looking for an additional partner to improve its bid forPioneer. It could also try to join forces with either Aberdeenor Macquarie, according to another source.
According to sources, Amundi, the Poste-led consortium,Macquarie and Aberdeen Asset Management have all gained accessto the data room of Pioneer, which manages over 220 billioneuros in assets and has three main offices located in Milan,Boston and Dublin.
Binding offers are due by Nov. 3, one source said. A finaldecision by UniCredit is expected after a Dec. 4 referendum onconstitutional reform that could unseat Prime Minister MatteoRenzi's government, creating financial market jitters that couldaffect UniCredit's fund-raising efforts.
Mustier will unveil his new strategic plan on Dec. 13.
($1 = 0.8957 euros) (Additional reporting by Elisa Anzolin; Writing by FrancescaLandini; Editing by Susan Fenton)
