* Investa shares hit highest level since 2008
(Recasts adding market reaction, analyst quote and background):
SYDNEY (Reuters) - Buyout giant Blackstone Group LP (BX.N) said it was willing to lift its bid for Australian landlord Investa Office Fund (IOF.AX) to A$3.3 billion ($2.4 billion) on Thursday, to beat a rival offer from Canada’s Oxford Properties Group. The bidding war heats up the tussle for the owner of 20 office towers as commercial rents boom, especially in Sydney where Investa’s holdings are concentrated and downtown capacity is tight.