US private equity giant Blackstone (BX) on Wednesday said in a sternly worded letter that a competing bid for Australian office real estate investor Investa Office Fund was not superior and that it reserves the right to cancel its bid should the company back out of a planned acquisition.

Blackstone had originally offered $5.25 a share for the Australian company, but late last month sweetened its offer to $5.45 a share, garnering the approval of the company’s board.

Canada’s Oxford Properties Group, however, on Tuesday sent an unsolicited bid to Investa for $5.50 a share, valuing the company at $2.4 billion. The Investa Listed Funds Management Limited (ILFML) board, which is responsible for the Investa Office Fund, said it advises shareholders to “take no action at this point” and still recommends the Blackstone offer as the superior proposal. Still, the board is “considering” the Oxford proposal.

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Blackstone said in its letter, which was made public, that Investa’s consideration of the alternative proposal from Oxford “will provide uncertainty to IOF unitholders.”

Still, Investa said its chairman will adjourn a planned meeting on Thursday in which shareholders were expected to approve the Blackstone proposal to allow the board time to consider the Oxford proposal and update shareholders accordingly.

In its letter, Blackstone said it reserves the right to claim a break-up fee should Investa’s board deem the Oxford proposal superior.

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